That 3D wiimote hack by Johnny Lee is simply awesome!
Nice drawing btw liudr! I was thinking maybe you can triangulate with 3 ultrasonic rangefinders? One in three corners of the display. I'm not sure how well it would work though, as your head is presumably attached to something also reflecting those sound waves 
That could probably be compensated for in the triangulation calculation somehow. But then there might be more than one person looking at the screen.
And I agree with tacoma.