In a year, I've used it for 81 hours and 55 minutes: thirteen and a half minutes a day, so a half-hour session three times a week. The Wii, game and telly cost about as much as a year's gym membership, and at the end of a year I still have them. I weighed 97.2kg the morning I first used the wii, and 94.6kg this morning; I have got down to 91kg in between.
I've got good at the boxing and the hula-hoop exercise; I still can't reliably head those blasted footballs, and the muscle exercise where you repeatedly and as fast as possible switch between lying on the ground holding one arm vertically up and standing up with the same arm held vertically up remains strikingly uncomfortable.
Wii's distance units are clearly a slightly different size from everybody else's, since a four-star rating on the free running seems to require you to do two miles in ten minutes; I can do what the Wii claims to be 3k in ten minutes, which is still vastly better than I could imagine doing on a real track.