I got one after DS was born in Jan 08. I used it quite a bit while he was immobile but once he started getting around it came out much less often! It's fun and easy enough but the same willpower is required to actually get going and use it as going to a gym! I think the games have improved a lot since it first came out, the one I have has very simple step classes and yoga on it. It's good for weighing you and setting yourself little goals (or big ones) over time periods.
Before getting pregnant, I used my Wii Fit pretty regularly for about six months and lost getting on for 2 stone. Mostly I did running, step, boxing and a bit of yoga but also used to vary occasionally with some of the odder exercises (like cycling and skateboarding). I lost loads more weight doing Wii Fit than seeing a personal trainer at the gym. Strange but true.
Fitting in 30/40 mins here or there did seem much easier then than going to the gym. Not sure whether that'll still be case with a little one, but at least it doesn't mean having to leave the house.
I recently got mine, although the motivation is waining as pregnancy gets worse. But on the plus side, DD of 3 also loves it, and plays several of the games with me. Even DP joins in when it's set up and ready (would never get it out on his own though).
I'd say yes, but make it as easy to turn on as possible (have the balance board quickly accessible, not tucked in a cupboard, and the console plugged in and ready to go).
The Wii Fit is fun, but not a very good workout. You can't link together all the exercises, so it's very stop/start. If you want a halfway decent workout with the Wii, get Just Dance/Just Dance 2, etc, something like that.
goodlifemummy, the Michael Jackson game is winging it's way to my house this Christmas, courtesy of a lovely relative of mine.