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.
i think 3dv built the depth maera, they apparently had a some sort of 3d webcam lined up but then ms bought them (see http://en.wikipedia.org/wiki/ZCam) in any case, i hope licensing wont be a problem
the face recognition login would be really great, but also think of what you could do with the POV/head tracking.. you could make sure messages appear where the user is (or is not) looking [on a multimon system for example] you could "peek" outside the edge of your desktop by meaning to the opposite direction
also, because you sit much closer to your pc than your tv, the depth resolution (in x/y) should be higher so maybe you can have it track your hands and fingers.. if thats possible, imagine the a 3d modeling app where you actually use your hands to manipulate your model just beeing able to do minority report type manipulation on the pc would be great
maybe i shouldnt get to exited yet though the word is still out on accuracy and resoultion i suppose