I already have the Wii, got it for Christmas. I find it to be enjoyable and fun, maybe it's not perfect, or even close to perfect, but it's new technology. It will take some time for Microsoft and developers to make games for it that will be a lot more responsive. I've heard a lot of praise about Dance Central (I have it, just have not yet played it yet), and that is probably due to the responsiveness, as if there was a very bad response time, then people would become frustrated and stop playing.
The only thing I dislike about the Kinect at this time, is the lack of games and apps for it. There's only a handful of games for the Kinect right now, most of the games are either unappealing or don't seem worth it. Several games seem worth it or at least decent (at least to the average gamer). There's some games for people who want to try and get into fit with the Kinect, then there's just games that are testing out the capabilities of the Kinect.
Overall, I believe the Kinect can become a pretty great thing, it just needs time and developers wanting to develop their games on it. I just hope there will be continued support for the Kinect in the months to come.