As many have said, this is clearly Microsoft and Sony trying to get some casual players on their side and maybe shoot Nintendo off the hegemony it's had this generation in terms of sales.
As for Natal's technology, it seems impressive enough (if you forget about the E3 catastrophe), however, without a price tag it's hard to determine if it's gonna be worth the money and the fact that early adopters will of course be guinea pigs. I heard somewhere that it was gonna be around US$70, which would be a decent amount. Now, if marter is right and it's around US$200, I'd pass. Being a PS3 owner, I'd have to pass on the Sony Motion Control, which is pretty much the same.