The Word of Notch has a "trickle" of information about the eventual version 1.8 "Adventure Update" for Minecraft, the sandbox adventure game:

The update is pretty big, and will change a lot of how Minecraft is played, focusing on making exploration and combat much more rewarding, and bringing in a bigger sense of adventure to the game.

Already implemented are new complex terrain features, at least one new mob, some interesting new combat mechanics, a new lighting engine, and some experimental new gameplay ideas. To come is more interesting farming, bigger incentives to explore, and npc villages.