They're adding a lot of new things to Minecraft, and they're letting us test them via dev snapshots! New biomes, new items, new blocks, a dedicated (custom) key for sprinting, and more.
Minecraft : 1.7 Snapshot : 13w36a : New Biomes! New Blocks! More Fish! Sprint Key! - YouTube
Minecraft : 1.7 Snapshot : 13w36a : New Biomes! New Blocks! More Fish! Sprint Key! - YouTube