Here's an interesting project worth keeping an eye on. It was built with openFrameworks using the ofxKinect addon. The user appears to be able to hover his or her hand over a particular vector on the screen in order to start playing a pre-set sample of music. The user can then move to another area and have that other sample play in tandem with the original, stop either one by moving away, or initiate a new sample.
Switch Music Conductor