I was curious whether anyone else here uses some form of head tracking like TrackIR or Freetrack.

I use Freetrack in ArmA, FSX, and Falcon 4.0, but I also like to finding interesting uses for it in other games. Even if it isn't used for controlling your view I sometimes find it useful to have a hands free method of control for stuff that doesn't have to be that precise, especially for games have a lot of controls.

http://www.free-track.net/

http://www.naturalpoint.com/trackir/