This was on slashdot a long time ago:
http://www.ischool.berkeley.edu/~ping/peep/
I think the n800's webcam would substitute nicely for the optical mouse used in one of the setups. It also appears that the clie used has a camera, but glancing over the paper it did not appear to be used as a tracking device.

Is any work being done on this? I know some people have the right idea
http://www.internettablettalk.com/fo...6566#post26566

I found https://garage.maemo.org/projects/motiondetector/ but this does not appear to do any scrolling or panning.