Very interesting: Surface tracks shapes with its vision system. There are five cameras in the Surface. The system has a very high resolution (dice can be tracked). Surface uses high-power leds with a mirror system.
I am going to present a few projects on my blog in which I collaborated in one or the other way. The project UNFOCUS – FOCUS is a multi-touch and TUI project that makes use of our fiducialtuioas3 classes.