Dang it i had a giant post and it went away dang it.
Well to summarize, sort of. The old post was like at least 3 times larger.
Villagers trade now with the new emerald or that is more rarer than diamond. They have a trading thing only open for so many trades, aka they run out of stock, and the more you trade with a villager the more options he has for trades.
They start with only one but if you trade them 3 times with that 1 thing they open up another thing you could trade with them. etc till like 4-5 things. and the things they trade are based on what they are, aka the blacksmith offers armor more often and can repair things too i think. Maybe. And the librarians like paper and books. Villager eggs now spawn random professions instead of the generic monk brown ones. Finally a true source of getting chainmail.
The village types change on biome, a few things like buckets and signs now stack, and now pre built features like pyramids and temples in biomes that are trapped.
BEST THING SINCE SLICED BREAD, NON HOSTILE MOBS NOW DON'T PUSH YOU AROUND!
Large biome world type. Makes biomes 16 times normal size.
Hardcore server setting now. You die you get banned.
Editable books and a change to book recipe. Stock up on them before the change. They now will cost a leather to make.
Trip wires, for cool new traps, it gives off a current on tripping.
Various name changes, like Spruce wood instead of just wood.
Lots of changes to enchanting. Max level 30 and a simpliar level curve.
Very cool enderchest. Eye of ender surrounded by obsidian, you put a block in one enderchest, you can open another enderchest elsewhere and take the block out. Works through dimensions afaik so put glowstone from nether in enderchest in nether. Go back to house and pull out the glowstone from there.
You get xp for mining or and furnaceing now, its a small amount.
Many cool changes for boats, there steer a lot better and don't crash on lily pads. and they can be deployed out of dispensers.
Dispensers can now be use and triggerable sources of lava and water.
Small changes to creeprer damage, its based on difficulty. Diamond armor and hard full blast is 2 hearts
Adventure mode in which you can kill but can't mine blocks. perfect for a capture the flag like thing, aka steel the wool block from a chest. well thats my own idea but yeah, anyways.
Wood blocks rotate like pistons, aka the end with the rings isn;t stuck facing up anymore.
Cookies heal more hunger and cocoa comes out of jungle tree leaves, and can be grown too iirc.
And many more bug fixes.
For more info
http://www.minecraftwiki.net/wiki/Version_history/Development_versionsView the 1.3 snapshots, 12w15a and on.