I've just been shown a really cool video from TED demoing a 'sixth sense' device. The prototype uses a projector to draw a UI on any surface (e.g. a wall, paper, even a hand) and then a camera recognises the interaction with that surface. It can even recognise gestures so a user can create a frame with their fingers and take a photograph.

Check out the video at http://www.ted.com/index.php/talks/pattie_maes_demos_the_sixth_sense.html. It's really is inspiring to think that this technology is only a few years away!