The Natal is not the Eyetoy. It is a device with multiple camereas which works just like the IR bar which the Nintendo Wii uses with it's remotes. Except, instead of tracking just one IR light, it is tracking your 4 appendages, head and torso.
The technology has been around. It was developed by 3DV which Microsoft aquired. Or actually, I believe they did, but I'm finding it hard to find information other than "Microsoft set to aquire..." and I'm short on time.
Here's a demonstration of 3DV's fighting game:
http://www.youtube.com/watch?v=iNg9Q23aQcY&feature=related
Here's links from Ars Technica which states, "I played a boxing game that actually worked much better than even Wii Boxing".
http://arstechnica.com/gaming/news/2008/01/3dv-shows-off-wii-like-camera.ars
http://arstechnica.com/gaming/news/2009/05/microsofts-big-surprise-at-e3.ars
Now, I'll be honest, I think Wii Boxing has abysmal controls, but it's also a shit-ton of fun. This could be amazing. It may not be able to handle motion like the Wii (especially with motion plus), but it kicks Eyetoy's ass.
