Previously, Elliott Woods used Kinect to (sort of) bring the hadouken into the real world. Now, modder "demize2010" has gone the other way, bringing gesture controls into Street Fighter IV. Using Kinect and the FAAST software, he's mapped Ryu and Ken's moves to specific gestures, so that the game character punches when he punches, throws a fireball when he pantomimes throwing a fireball, and so on.
Basically, it's what we all thought the Sega Activator would be. If you'd like to try it out yourself -- and you have a copy of Street Fighter IV for PC, of course -- you can find a file with the specific key bindings on the Kinect Hacks site.