Kosmix now has a Wii Fit at the office. It was interesting, but nowhere near as addictive as the original Wii sports.
Will it help people get fit? My 2 cents on this - Wii Fit will not be for those who go to the gym or work out even thrice a week. You could burn a lot more calories much faster at the gym... and cardio machines today do have some distracting stats displays to satisfy that need.
For those who don't work out regularly, or are busy, lazy, or not near a gym, the Wii Fit can be a good motivator to get some exercise while having fun, and charting performance.
Forecast - look for women aged 35 - 50 to be the primary users.
And finally, a funny video courtesy of Dan Hendricks - http://www.youtube.com/watch?v=_iYBmAVuBns