A friend wanted to know these, these are for my room, so here they are for your reading pleasure. Feel free to contribute if you have Kinect set up in your abode.

Space across: 8.5 feet or 2.56m
Space towards Kinect from back wall: 9 feet or 2.74m
Minimum space towards Kinect from you the player as set by Kinect Adventures (varies from game and mini game): 6.7 feet or 2.00m
Height of Kinect from ground (Remember Kinect should either be very low or very high. I place it high cos then I can have it behind the TV): 6.7 feet or 2.00m

IMPORTANT!: If you place Kinect even higher, then you should be able to stand closer than 2 metres. Which is something I should try, come to think about it.

edited:

Probably if you put TV right below the sensor, which I can't do, then you can get what Microsoft says: 6 feet distance from the sensor and player.