Here is what is in 1.3 which is found in the spoiler. Man there is a whole lot of goodies.
I am now giving it a work over to see what is new (that should take me about 5 or so years).
SPOILER: SHOW
Note : Very few references are provided here since most of this content has been directly released in weekly snapshots 12w15a to 12w30e.
General
Improved overall stability and performance
Reduced CPU, RAM & bandwidth usage
Accelerated chunk loading
Decreased lag spike frequency
Made the Nether less laggy
Decreased unnecessary world updates
Made the chat work smoothly even when the server is laggy
Decreased packets sent between client and server
Made Singleplayer internally use a Multiplayer server[1][2]
Decreased world saving intervals
Added optional single-player commands called "Cheats" on non-hardcore worlds[3]
Type / and then hit tab to autocomplete & get help on various commands
Most commands from MP are available
Added option to let LAN friends join SP games
You can choose which gamemode players join in and whether they are allowed to use cheats
Added demo mode for non-premium users[3]
Lasts 5 game days per world
Added Chat Settings
Change which parts of chat are shown and how opaque it is
Toggle chat colors, links being clickable and warning prompts for links
Option to rebind the command key, which opens the chat with / in the textfield
Added Snooper Settings
Allows users to toggle anonymous data being sent to Mojang
Shows which data will be sent
Added video options
Have to be toggled manually in options.txt for now
VSync
Fullscreen mode
Mobs can now spawn on top slabs and upside down stairs
Improved F3 mode:
Truncated coordinates to 5 fractional digits
The y-coordinate now shows both the feet level and the eye level
Removed frame rendering time history graph (bottom-left)
3 new values:
ws: Walking speed (constant)
fs: Flying speed (constant)
g: Boolean value, true when you touch the ground
Updated language files
Added tooltips for all types of Monster Egg blocks and the End Portal Frame
Added more descriptive tooltips for different types of tree-related blocks, sandstone and stone bricks[4]
Localized server commands
Added missing commands-related strings
Added missing double chest GUI caption
Fixed many bugs
Fixed texture packs in folders not showing their icon and description
Fixed Man-in-the-middle attack allowing hackers to log in as you when you visit their server
Fixed the Open texturepack folder button not working on OS X
Gameplay
Added Adventure mode[5]
Only playable using commands
Building, setting things on fire and using buckets is disabled
Players can only interact with mobs and the environment
Players can place and take stuff from a chest, a furnace or a dispenser
Added trading[6]
Using emerald as currency, villagers will, depending on profession, offer different trades to players
There are three kinds of trades: Selling, buying and enchanting
As displayed in the top-most part of the trading GUI, villagers take one or more items or item stacks and give back something
After trading, villagers will sometimes emit purple particles for a few seconds to indicate that their trades changed
Otherwise unobtainable bottles o' enchanting and chainmail armor can be obtained by trading
Improved Creative mode inventory
There are categorized tabs for various groups of items and blocks
Added a search tab which will automatically be switched to when the chat key is hit
Added survival inventory tab, which shows the full inventory, a 'Destroy item' slot, armor slots including a preview of your character and a 2x2 crafting field
Items can now be deleted from the inventory by shift-clicking them
Added layered snow block, Monster Egg Blocks (Silverfish spawning blocks), Ender Portal frame and all potions[7]
Now shows potion effects' timers like in Survival
Improved experience collection
Depending on ore type, experience now drops from ores that drop items
Taking smelted items out of furnaces gives experience now
Destroying mob spawners gives experience now
Adjusted experience level progression:
Levels 1-15 cost 17 XP points each
Levels 16-30 cost 3 more XP points than the previous (cost = 17 + (level - 15) * 3)
Levels 31-∞ cost 7 more XP points than the previous (cost = 62 + (level - 30) * 7)
Improved enchanting
The new maximum level with bookshelves is 30, without 8
15 bookshelves are enough to reach level 30
The 3rd slot shows the most expensive possible enchantment more often
Increased chances for multiple enchantments at once
Adjusted enchantments' to go with the new maximum level
Added writing in books
New crafting recipe for books: 3 pieces of paper and one piece of leather in any possible shape
New item: Book and Quill - Crafting recipe: 1 ink sac, 1 feather and 1 book in any possible shape
Right-click to write on & edit up to 50 pages or read
Click 'Done' to save the book, 'Sign' to choose a title and finalize the book
Improved Multiplayer
Made entities less likely to glitch through blocks
Added automagical downloading of standard sized texture packs when joining servers
Made server commands more descriptive
Added reason parameter to /ban
Added /seed command to show the map seed
Added /defaultgamemode command to choose the gamemode new players start in
Added /debug command to enable and disable profiling
/kick messages can now contain "\n" to force a new line
Blocks other players are mining now show cracks[8]
/tp can now be used to teleport to specific coordinates
Made server list re-orderable: shift+click or shift+arrow keys move selected servers
Server list now scans for LAN servers
Added hardcore difficulty: Players are banned upon death[9]
Added SRV Record Lookup support
Different subdomains of one domain can handle different servers via different port numbers.
Service name should be "minecraft"; ie "_minecraft._tcp.example.com"
Added & changed many minor things
Individual, stackable items near each other on the ground now become one item stack
Added shift clicking support to armor slots, brewing stands & enchantment tables
Added setting to disable servers offering you texture packs
Made the stars smaller and brighter[10]
Villagers spawned from spawn eggs will get a random profession now
Removed the downwards knockback while drowning
Doors being broken by zombies now show their damage
You now spawn with an empty inventory in Creative mode
The "Mojang" splash screen when opening the game appears for 1 instead of 3 seconds now
The sky color in the End changed
Improved the Pick Block key
You now get the actual block
You can now pick paintings, boats, minecarts and mobs, which will give you their spawn eggs
Picking huge mushroom blocks now gives mushrooms
You can no longer pick portal blocks
Fixed many bugs
Fixed flying slowly in liquids
Fixed blocks with the same id but different data/damage values stacking in Creative inventory
Fixed boats & minecarts not being one-hit breakable in Creative
Fixed raw fish, dyes, saddles, potions, milk buckets and tools depleting in Creative
Fixed water destroying non-solid blocks when breaking them from above
Fixed Silk touch giving you only one slab from double slabs
Fixed redstone updates not propagating through unloaded chunks[11]
Fixed repeaters getting stuck when loading their chunk
Fixed tools taking damage when breaking insta-breakable blocks
Fixed ender pearls and eyes of ender not being aligned in the inventory
Fixed the arrow representing players on held maps being offset
Fixed being able to duplicate sand, gravel and powered rail
Fixed placing a piston in front of another powered, but not extended one resulting in a glitched piston with the head's texture on all sides
Fixed TNT dropping as a resource on creative mode
Fixed powering specifically glitched pistons crashing the game
Fixed the End Portal Frame block not showing as a block in the inventory
Fixed weather not working correctly in certain biomes
Fixed Overworld portals above Y=127 not being recognized when leaving the Nether
Fixed various hacked mob spawners crashing the game
Fixed thrown splash potions not preserving their type when reloading the world
Fixed many Multiplayer bugs
Fixed arrows scooting up to the top of the block they were shot on
Fixed endermen not opening their jaws
Fixed fully charged arrows not showing their particle effect
Fixed many sounds not playing[12][13][14][15]
Fixed magma cubes' and slimes' jumping animations not showing
Fixed thunderstorms not darkening the sky
Fixed weather not fading in or out
Fixed enchanted armor and tools not glowing to other players
Fixed explosions not pushing players back
Fixed TNT not knocking back players
Fixed pistons not pushing back players
Fixed players on minecarts, boats or pigs and spider jockeys not being displayed in the correct location
Fixed glitchy mob prediction[16]
Fixed fishing lines not showing[14][17]
Fixed sneaking players' nameplates not staying hidden when loading the chunks they are in
Fixed Unbreaking-enchanted tools sometimes breaking and then re-appearing a few times
Fixed potion effects losing their graphical effects when traveling between dimensions
Fixed blocks disappearing when placing them under yourself and jumping
World Generation
Made sub-biome type mountains like Desert Hills or Ice Mountains taller
Made cocoa beans appear on some small jungle trees
Added optional starting chest on non-hardcore worlds[3]
Contents: wooden & stone tools, bread, apples, logs, planks and sticks
Added large biomes world type, increasing biome sizes immensely[4]
Added desert-specific villages
Added Desert Temples
Built out of various kinds of sandstone and wool
Include hidden chest room and TNT trap, with loot including rotten flesh, bones, iron ingots and gold ingots, diamonds and emeralds
Added Jungle Temples
Built out of various kinds of cobblestone
Contain multiple tripwire traps triggering dispensers filled with arrows
Loot chests include bones, rotten flesh, gold ingots, iron ingots, diamonds and emeralds
Added emerald ore
Only generates in Extreme Hills biomes
Occurs up to 8 times per chunk in veins of 1
Generates between layers 4 and 31, inclusive
Blocks & Items
Emerald Ore
Drops Emerald
Emerald
Is used to trade with villagers
Block of Emerald[18]
Crafted by putting 9 emeralds on a crafting table
Ender Chest
Crafted by surrounding an eye of ender with 8 pieces of obsidian
Stores each player's contents across dimensions and all Ender Chests
Contents are preserved even if all Ender Chests are destroyed
Explosion-resistant
Emits light and purple particles
Unless mined using a Silk Touch-enchanted pickaxe, they drop 8 obsidian[19]
Tripwire Hook[20][21]
String in between needs to be placed manually[22]
Breaking the string triggers a redstone signal, cutting it using shears doesn't
Entities like boats, mobs, arrows or players touching the string trigger a redstone signal[23]
String can be up to 40 blocks long[23]
Crafting recipe: Iron ingot on top of a stick on top of a wooden plank
String
Can now be placed on the ground decoratively
Wooden logs
Can now be placed in 3 different directions
Placement works like similar to piston placement
Furnaces
Can be fueled by wooden tools now
Return an empty bucket when using lava buckets as fuel now
Ice
Instead of melting in the nether, it now disappears
Can be obtained using Silk Touch-enchanted gear now[24]
Glass Panes
Can be obtained using Silk Touch-enchanted gear now[25]
Nether portal
Leaks into the Overworld now: Depending on difficulty, zombie pigmen rarely spawn in them
Slabs
Added all wood types
Wooden slabs crafted after the update act like wood
Stairs
Added Sandstone Stairs
Added wooden stairs for all kinds of wood
Adjusted hitbox
Slabs and Stairs
Will now be placed upside-down when placed on the upper half of a block's side
When placed upside down, rails, pressure plates, levers, doors, torches, redstone torches, repeaters, redstone dust and beds can be placed on them - Redstone dust behaves like on glowstone - It transmits power horizontally and upwards, but not downwards. Redstone torches don't power redstone placed on slabs/stairs above them.
Leaves
Water slowly drips through them when it's raining
Cauldrons
Slowly fill up when it's raining
Dispensers
Minecarts & boats will now be placed if there's rails/water in place
Instead of dispensing buckets, dispensers will now suck in or place water or lava in front of them
Gravel
Changed texture
Jungle leaves
Have a 1/200 chance to drop a cocoa bean when destroyed now
Lever
Can be placed on the ceiling now
Wooden pressure plates
Are triggered by arrows now
Pistons
Now take 0.05 seconds to expand
TNT
Depending on difficulty, does different amounts of damage now:
Peaceful: no damage
Easy: ~50% less damage
Normal: same damage as before
Hard: 33.3…% more damage
Cocoa beans
Retextured item
Can be planted & grown on jungle wood now
Can be grown instantly using bone meal
Cookies
Give a full hunger point now
Nether Warts
Can now be grown in the Overworld and in the End
Book
Changed crafting recipe: 3 pieces of paper and one piece of leather in any possible shape
Book and Quill
Crafting recipe: 1 ink sac, 1 feather and 1 book in any possible shape
See above for more information
Written Book
Can only be obtained by signing a Book and Quill
Can be sold to villagers
Empty buckets
Stack up to 16 now[26][27]
Stacked buckets work just like stacked glass bottles do
Signs
Stack up to 16 now
Crafting now gives 3 signs instead of 1
Golden Apple[28]
Has two crafting recipes now, the new one replacing gold nuggets with gold blocks
Second tier gives Regeneration IV, Resistance and Fire resistance effects
Only second tier glows like enchanted tools
Has attributes the Golden Apple had before 1.1[29]
Spawners
Added NBT tags to further customize spawned mobs
Only changeable using map editors or mods
Boats
Are not broken by lilypads anymore, instead they run straight through the lilypad now, breaking and sometimes dropping it
Are less glitchy and more responsive now
Increased maximum speed
When exiting, players will be moved from the boat
When broken by a player, they drop a boat now
Minecarts
When on rails, they can be accelerated a bit while sitting in them
When exiting, players will be moved from the minecart
Mobs
Pigs
Drop 1-3 meat now
Slimes
Reduced spawn rate in superflat maps
Silverfish
When suffering from poison potions, they will now spawn more silverfish from nearby silverfish blocks more often
Creepers
Increased knockback effect
Depending on difficulty, they do more damage now:
Easy: ~50% less damage
Normal: same damage as before
Hard: 33.3…% more damage
Creepers & Spiders
Become aggressive towards the last mob or player that hit them now[30][31]
Skeletons, Creepers & Zombies
Become neutral against players again a few seconds after being hit in Creative
