MS didn't invent this technology, they are licensing it.
ms bought the company [3DV] that built the 3d camera
As far as I know, 3DV didn't build Natal, and Microsoft didn't license it. It was built by Microsoft, and they bought 3DV to prevent others from licensing similar technology. See here. Even if the hardware is designed by 3DV, they didn't license the technology, they bought it. (3DV sold all their assets to Microsoft after all.) So using it on Windows shouldn't be a problem licensing-wise.
I'd love to see some drivers for it. It should be able to solve the old 'I don't want to sit with my arms outstretched' problem people apparently have with touchscreens. And using it for media center would be awesome. Flip through your albums, make a hush-hush gesture to turn down or mute the volume, throw up the horns to play your death-metal playlist...
Also, I'd want this to happen if only for the facial recognition. Sit down in front of your PC and hey, you're logged in. Sounds awesome.