I tried a bit but something about it didn't tickle anything fancy so just dropped it.
For the facetracknoir, I played around with a bit last year or so, for it being a way to get head track essentially for free, it's pretty damn amazing.
That said, the output from the faceapi is extremely jittery, although he has all sorts of sliding averages to smooth out the numbers jumping, it is really difficult to hold your vision steady in one direction. Your head isn't moving but the faceapi keeps sending new x/y/z outputs regardless.
You can try to deadzone it, but if it goes too high you lose the good response time of shifting your head around a bit.
I tried with a logitech webcam @ 30 FPS, which was nice in that I could adjust the camera gain and all that to get better result in low light. I had a crappy desk lamp behind me off to the right, and if that is the only light source it really confuses the face algorithm with the heavy light on one side of your face. Again this was a problem for me because I have no lamp behind me and tend to play at night with lights off in the house.
I then switched to a ps3 eye to get the higher framerates, I think I got around 50ish, which is very noticeable in response time for glancing around, but still has the same drift problem. In addition the eye has a wider lens so it was picking up more junk behind me, at one point it thought a picture on the wall behind me was the face, in addition the software for the ps3 eye I couldn't find settings for the camera's gain and such so couldn't tweak it for low light either.
All in all you can't beat a track IR's stability, but as it costs an arm and leg facetrack is a great alternative.
/Am waiting on occulous rift