qole,
yes the multitouch is uncalibrated and raw and will never be 100% pixel perfect, but its relative to your finger and gives enough to demonstrate principles or allow additional ui interaction if so required.

The main problem with the technique at present is handling the edge cases towards the start and end of the touching, but thats a filtering problem rather than anything.

If i had bitmap rotation code in place I would have tested with that to see just how stable it can be made, I'm hopeful it can be made pretty slick