an accelerometer could be used for image stabilisation, auto-rotation of the screen, navigation dead-reckoning when GPS loses fix (or to save power in GPS by allowing chipset to sleep), games and gimmicks, HID (shake to control media player) etc.

on the subject of the webcam in the N800, it's poor probably for two reasons, one is the tiny lens, 2nd is the tiny sensor. I wonder if the circuitry could be re-purposed for something more useful, such as an additional USB port or high-voltage taser-like probe :-)