Head tracking obviously tracks your head but why? It is used to change the perspective of 3D object shown on a 2D screen, the video link below demonstrates this extremely well.
If you don’t know what head tracking is you may want to watch this example of the same concept using the Wii but explained in detail.
Another virtual reality post but from a completely different perspective (pun intended). This concept is explored in a few released games but is not heavily used; most likely because the 3rd person view (people on the couch) is nauseating. For a single person being the only one in the room while playing this is great and is a real leap to VR – again without wearing anything – but will most likely never be heavily used in games.
Find a better Kinect example? Find a head tracking video posted before this one, higher quality, or longer? Post it in the comments?