I rewrote the I Eat Beats project so I could use a linear polarizer with the webcam to cancel out the screen. Now there are a bunch more things you can do, like visualize the state of the sensors/interface elements more clearly. I'm also using color now.
First half shows classic I Eat Beats setup. Second half shows a control surface for the Malstrom in Reason. Sliders left to right: osc a octave, osc a semitone, osc b octave, osc b semitone, mod a rate, mod a pitch, mod b rate, mod b volume. The two knobs on the right encode portamento and volume. The buttons on the top enable/disable the oscillators and modulators.
I'd like to see a stop-motion animation interface that uses this technique, and lets you "onion skin" with real-world objects.
I wanted to share this at SIGGRAPH this year, but I only got about 2/3 of the materials in on time :(