check out the link below.
http://www.youtube.com/watch?v=Jd3-e...layer_embedded
I got it from an AI story about Apple filing a head tracking patent application. I'm not saying that they would do this, but it certainly falls into the camera's already there so might as well sue it scenario.
The 3-d effect is quite convincing, but it only works for the person being tracked, which is just fine for a personal computer... What's really neat is that it allows the display to be much more like a virtual window than the current metaphor, which is more like a desktop or corkboard.
Properly constrained it could make for a very neat UI experience too. Imagine looking behind open windows, or pushing some menus off to one side and just leaning over to get a look at them when needed...