FaceOSC is a tool for prototyping face-based interaction. It's built on non-commercial open source FaceTracker code from Jason Saragih. Download it here:
FaceOSC comes as an example app with the ofxFaceTracker addon for openFrameworks.
OSCulator is an excellent program for routing OSC and MIDI. Download it at osculator.net/
Some of the "face gestures" (or metrics) are more stable than others. Lighting can also have a huge influence on the stability of your values: even lighting from the front coupled with a dark background can give the best results.
Some of the first demos from others: