I found this cool video via @Psicoff on Twitter. It's a video by Steve Fredom using a web cam as a Theremin.
Ableton Theremin – experimental electronic music made by translating hand gestures tracked by Quartz Composer and webcam, into OSC then Midi and sending on to Ableton to trigger Spectrasonics Omnisphere and RMX.
I'm doing similar spatial control with AudioCubes and Theremin (pitch-to-MIDI) into Live and simply love the possibiliites of openning this up to more people via built-in web cams.
Artist site: http://www.markmoshermusic.com
Host of Sonic Encounters Podcast: http://markmoshermusic.com/podcast/.
Boulder Synthesizer Meetup founder and host: http://www.bouldersynth.com