Moving away from "immersion" discussion (anyway I agree with commodorejohn), 10 days ago I tried the XBox 360 with Kinect in a superstore: well, despite I consider a nice option, it didn't impress me that much regarding responsiveness.
I played a bit with "Kinect Aventures" and I found it unresponsive to my movements especially with the ball game, a sort of Arkanoid/Breakout where the bat is you with your body.
Moving my arms, and legs especially, got a clearly delayed movement in the game.
I don't know... maybe needs some more processing power and/or improvements?