Jens Bergensten has been teasing new systems (via Twitter) of trading and currency which he has plans to implement into Minecraft at some point in the near future.
The system will allow players to trade with each other, and with NPC villagers, making the game more of an RPG than ever. Once the system is in place, players will be able to barter items and trade coins for equipment. The implementation will also provide villagers with a purpose besides milling around aimlessly.
In addition to the new teaser, Jens Bergensten's screenshot includes some new textures for gravel. It's not much of an update, but it's a nice improvement from the usual mess of noise.
Bergensten is now the head of development on Minecraft, succeeding Notch as the game's frontrunner. Notch has since shifted his eyes onto the development of 0x10c, which is a game about spaceships.