trackir could also be used to create quasi3d displays.
Small changes in viewing due to head movements give us important clues about the distance of objects. WIth trackir, one can display slightly different images depending on the viewers position.
This will fake the brain into thinking it is looking at something 3d.
Two applications of this:
1) 3d desktops (recent slashdot)
2) doctors viewing medical data, such as computer x-rays. Hands-free is of course useful.
I would be interested developing this further, but can not spend much time on it.