Seb Wills has hooked the accelerometers in the Toshiba M200 to control the Dasher text-input system (in which letters gradually slide from right-to-left and your vertical motion selects them). Fantastic!
One of the most interesting things about the Tablet PC is all the ways we search for alternate input techniques. Personally, I find that SHARK has the highest rate of entry (better than FITALY, better than Dasher, way better than handwriting), but there are aspects of the Java-based input panel that are really frustrating.
For my next DevX article, I'm working on a voice-input correction system that is based on the Tablet PC Input Panel, which is a tremendous piece of UI engineering for correcting hand-writing. My premise is that it's acceptable to use a mixed-mode editing panel, where a pen / mouse is used to navigate the recognized text and its alternates. I'm having some trouble understanding the SAPI object model -- I'm requesting alternates but getting identical outputs, which is strange.