I don't think Kinect will provide the kind of push in sales Microsoft is hoping for, but I think it will accomplish something. They do need to appeal to hardcore crowd more with it, though.
Anyway, I sincerely hope that the Xbox360 and PS3 both last for at least 10 years. For once, I'd like to see the industry actually wait until it's actually logical to make the move to a new generation. Notice that I didn't mention the Wii. I think that a follow-up to that is probably sooner on the horizon than replacements to the Xbox360 and PS3. The next system will likely just put it in a similar league with the HD consoles, meaning there's no reason for MS or Sony to jump to the next stage.
There's still a helluva lot of room for expansion and growth in this generation--and I'm extremely pleased to see Microsoft and Sony looking to expand the lifespans of their machines rather than jumping ahead prematurely. I still believe this current generation was started about two years too soon, which is why so many companies struggled so severely during the change. Nobody was really ready for it.
The longer this generation lasts, the better prepared we'll be for the next one.