This is supposedly video of somebody playing Geometry Wars on Project Natal. Emphasis on the supposedly, in case you missed the italics first time around.
A Destructoid reader reckons this was shot at a "Christmas Party", though that's where the information dries up. On the "could be" side of things, there's lag at several points, and even a freeze, both issues that are reportedly affecting early development for the camera.
On the "probably not" side, however, is the fact at several instances the movement of the guy's hands have no bearing whatsoever on what's happening on-screen.
Whichever the case may be, it's still an interesting look at how Natal has the potential to change the way you approach a game. Normally, Geometry Wars is a raw shooter, a seat-of-the-pants kind of affair. Combine it with Natal, though, and - provided that's how you'd actually control the game - it suddenly becomes a more synaesthetic experience, as you move from "player" to "conductor".
Is this a Natal-powered game of Geometry Wars? [Destructoid]