TBH for things like driving games surely the best technology will be a steering wheel with accelerometers in it, a la wii, rather than it noting where your hands are. Id imagine it would be fairly easy for them to code in an upper body or hands tracking script, rather than needing full body.
People that walk in front of me when playing games should know better.
And its just as likely for me at least to have people in the room try and grab my controller or throw things at me.
Im not a fanboy or anything, I wont be getting this any time soon after the release on the grounds of the xbox being in a room too small to use it