If you are planning on buying Kinect this fall there are a few things you need to consider and Microsoft have released some instructions on how to get the most out of Kinect.
First of all you need to have a clean floor in front of the TV (clean floors are pretty nice regardless), this is due to the fact that the camera scans the floor and uses it as a point of reference.
You should also place the camera in the middle of the screen, preferably on top of it (although when we've tried it has typically been placed below the screen). It should not stand next to a loud speaker or subwoofer as loud sounds interfere with the microphone.
To play the most movement based games it is recommended that you stand two metres from the screen and have about a metre of space on each side to move.
Finally you shouldn't have any strong halogen lights (spotlights) as they create uneven lighting in the room and this causes problems as Kinect attempts to scan your movements.