So it turns out that Microsoft aren't the only company with a body-tracking technology in their pocket. Israel-based Omek Interactive also showed a PC-based body-tracking motion control system at CES, although it should be stressed that this is a software solution. Omek claim their system will work with "any depth camera". That sounds good except - and I could be wrong - I can't say I'm aware of any cheap depth cameras on the market, other than a certain MS one. (John points out that ASUS have one coming.) Anyway, it functions... as you might expect. See the video below for shakycam footage.
Cheers to Dan for the link.