Combine gyroscope, accelerometer and compass, and you get very precise data about movement of the device. Together they basically enables you to do very interesting motion control stuff. Think an always-with-you Wii controller, but better.

I bet that there will be a lot of cool innovations coming. In the beginning, they will be mostly games, but it will be usable for many kinds of real world control tasks, too.

(More info about gyroscope http://forums.appleinsider.com/showthread.php?threadid=11060...)