Redmond's Surface Tabletop PC has garnered a lot of attention. While everyone agrees that it's awesome, no one can really figure out a practical and economical use for the device. However, a mobile version of the same software is another story.
TechFlash has a pretty nifty video of the technology in action. The set-up shows a camera, a projector and a cell phone. A projection of the cell phone display is made on a tabletop, and the user interacts with this projection image. The coolest part of it all is that you don't need to touch the image on the table to control things. The demo below shows volume being controlled with mid-air gestures.
Check out the video below.