Did anyone build an accelerometer-based mouse?
I actually worked on building this device about 10 years ago. Here's the company that makes them: http://gyration.com/index.php/us/home.html

You can buy them various places online, e.g. Amazon.

The internals are pretty cool-- they contain a pair of vibrating beams that change the amplitude of their vibration due to the Coriolis effect as you rotate them in space.