I picked up a Wii fit yesterday and after I set it up it told me I was overweight and had the characteristics of a 47 year old! I couldn't let a game tell me that so I started right away and setup a goal to loose a certain amount in 2 weeks - the wii will keep track of this. Overall the game is pretty sweet. I would have to say that my favorite has to be the balance games like ski salom and soccer, but I haven't fully played all the other games yet but soon enough I was sweating.
While some say that its not a true workout and I'm not saying it is, it definately burns some calories and most of all its fun. I'm actually looking forward to getting home and playing again today - something I cant say for going to the gym. There are also more games that are "Balance Board-compatible" some are already annouced EA' Skate It, Bandai Namco's We Ski, THQ's cheerleader game and I'm sure more will come out. There are already balance board hacks out there - like using the board to surf Google Earth with a hacked Nintendo Wii Board (video below) Im glad I picked it up.