Or any other firewire camera. Freeverse now has announced Toysight, which is a way to play certain games using your camera. I tried out the demo and it is pretty cool (though I'd think you look pretty stupid playing them). I was kind of amazed at how well some of the things worked. First you start up the game and it scans what it can see, then you step in front of the camera and as you move your hands a cursor will follow it. They've got a few kinds of controls you can use on the screen, like a slider bar. They even have a movie of it in action. Pretty keen.
Though I think it would be harder to sneak in a quick game of Marble Factory while at work.
