This is one of the cooler hardware hacks I’ve run across in the past few weeks: Turning a PowerBook into a Marionette. Unfortunately it’s motion detector specific, so no real chance of that being ported to other devices.
I’m still waiting for someone to take one of those new Lenovo X60 Tablets and make it into a giant Etch A Sketch. Lenovo/IBM’s motion detector (ADXL320 managed through the embedded controller) may be up to the task, but nobody has really done anything with it thus far, other than Knock-Knock by IBM.