On the other hand, how cool would it be to wave your hand in front of your computer to mute it, or to flip through slides by moving your hands back and forth? Think less full-body motions and more simply tracking the position of hands, allowing for touch-screen like interactions without actually needing to touch the screen. There are lots of things I can see this being really useful for (especially 3d modeling; I recently saw an article about an iPad program which lets you model as if you were working with clay, and I would love to have something like that for my PC).