As a prototype, this looks amazing, but I don't think I'd like to use that environment for more than brief interactions with the computer. Twenty minutes with one's hands in the air starts to become a strain, and a lot of that system's gesture recognition looks to depend on it.
I'm also a little dubious about how delicate and slow that 3D manipulation for cut and pasting text looked in the demo. I work in 3D a lot, and I'd never expect text to be difficult to move from one document to another.
Still, this is a prototype. As long as most gestures are kept to the desk surface, with only a few requiring movement in the up and down axis, I really want one.