The Fluid Interfaces Group at MIT's Media Lab has created "Mouseless" - a beta version of what computers might be like in twenty years. Watch this video of somebody controlling a cursor by moving an invisible mouse.
If you recall, this is the same group of students who created the Sixth Sense interface, where you can dial a phone by poking your hand, or take a picture just by holding up your fingers. That project, led by Pranav Mistry, was featured at TED and burned up the internet with its awesomeness. The invisible mouse is another extension of the ideas Mistry and the group played with in Sixth Sense. I can't wait for the experiments of this group to become a reality.