My girlfriend's housemate bought one so we played around with it last night.
As I can't use those crappy joypads consoles come with, the control system was pretty cool, but it was also a bit hard to really be accurate with it.
Also, we were only playing the games that came with it and a bunch of extra games on Super Monkeyball.
Probably beats Singstar for party fun, assuming you had 3 or 4 controllers. Not sure how long the controller gimmick would last in a normal one-player game, though.