I think that it's cool that sony are doing it, and it looks not only better than the wii but with the PS3 technology will blow it out of the water. Thing is, you also need a camera and this will be LOADS total. Also, there might be gimmicky crap- but the wii is much easier to develop on so the PS3 probably won't get much. And the controller looks terrible (although they said the design will change).
Anyway, it looks better than Natal- the precision is excellent and Natal basically just looks like another EyeToy, only slightly more accurate, although looking at the videos it seems like the wii when it was first released. It also seems like the xbox is moving towards the family range (shudder).
I'm all for the PS3 sensor- Natal looks weird, but hey, it's probably great. Sony do have a habit of copying things- a LOT of things.