Well I picked up Wii and WiiFit for my wife for Christmas and this is the basically one month experience.
Although my kids (3 boys 13, 11 and 7) have never asked for a Wii they were excited that mom got one. The initial week they played WiiSports a good deal (not as much as the Xbox 360 software they got for Christmas, but they played it.) and also fooled around with WiiFit. My wife and I played a WiiSports some as well and as for me WiiSports was really what I expected. Turning a button into a flick of the wrist. I could play and beat most people in really all the games without mimicing the motions of the real thing.
The big thing is that my wife and I decided to really give WiiFit a chance. That after all is why she wanted a Wii. We have been getting up an hour earlier each morning to each get 30 minutes in on WiiFit. We have both lost some weight. So I guess that as a exercise device the Wii and WiiFit is doing its job. As for a console the Wii doesnt get much use except for an occasional short play of WiiSports. Not intending on purchasing any additional software for the Wii any time soon. We received 10 Xbox 360 games this Christmas and that is more than enought for a good while.
Its libraries that sell systems not a single game.