I had the opportunity to try out the Kinect device for the Xbox at the new Microsoft store in Scottsdale's Fashion Square Mall this weekend. I highly recommend visiting the store if you live in the Phoenix metro area, San Diego, Mission Viejo, or Denver metro area. There was no one watching the Microsoft store employee playing with the game (prominently located right in the window for maximum exposure), but by the time we left there was a crowd of people around, and a line of people waiting to play. The employee was playing a driving game that actually looked quite complicated in terms of the motions he had to use to drive the car.
However, for us to demo Kinect, he pulled up the bowling game (what was odd is that he had to turn the system off and then back on before doing so). My 6-year-old was first, and easily picked up the directions on how to play (stand in a certain spot, raise your right arm straight out to "pick up" the ball, then throw like you normally would). We all got a turn, and the Kinect seamlessly transferred from one of us to the other, even though there was three feet difference in height from the shortest to the tallest of us.