I know this is cool. But really - who wants to graffiti their own living room - except at parties, you know good parties, parties where the wii would be locked up several streets away and the £2k projector taken to grans and the only 'graffiti' would be stuff about your mum on the fridge.
Oh, yes and at corporate conferences in the "chill out" area so people can 'bond'.
So tech +100; cool +100; usefulness -100; likelihood of ending up with the wiifit and the nunchuks under the sofa = very high.
[Also feeling sorry for some guys who demo'd their own version of this to us a few months ago and had clearly spent years on developing something no-where near as good as this]