I’ve started using a pretty good and free alternative.
You can use FaceTrackNoIR which is a free webcam face tracking application. I don’t have a webcam attached to my desktop so I’m using droid cam on my phone linked to my PC via wifi and it works great. The only downside is that the latency is higher than Track IR and of course it’s not 100% accurate, but it does the same job for free. The upside is that you don’t have to wear any markers or caps like you do with Track IR.
Link to FaceTrackNoIR:
http://facetracknoir.sourceforge.net/home/default.htm