My brother got one and I helped set his up. Within minutes my niece and I were playing Kinect Adventures and having a blast. I worked up a heck of a sweat before I even knew it.

If that experience wasn't enough to convince me to get one, this sealed the deal.
http://www.mattcutts.com/blog/open-kinect-contest/...

I haven't played the Your Shape game yet but my brother said it was awesome. The "zen mode" or something like that is what interests me most.