I think there may have been a topic on this at the old forum, but I just want to rave about the wii fit! I have never had this much success from a yoga or aerobics video, because the Wii Fit gives you feedback - it knows if you put your foot on the floor and tells you that you don't have your weight distributed correctly. It also does a balance test and it can tell that my left side of my body is off kilter, it also seems that it is improving (or I've just figured out how to make it give me a better reading?). It also takes you weight and tells you your BMI although it tells me that I'm underweight, because it thinks that a BMI of 22 is the healthiest, and mine is about 20.
I really like the step aerobics, it isn't too fast and it knows if you're doing it correctly, which is way better than a video, which usually just confuses me. I've done two rounds of physical therapy now and have to say that I feel like the Wii Fit is better for me - it got the point where I was paying a lot of money for them to just tell me to continue doing the same exercises. I can't do all of the activities on the Wii Fit, some are just not appropriate for spineys, but others are fine - in fact I unlocked one the other day that I did at both physical therapists and the chiropractor.
Anyway, just wanted to share my experiences. If you don't already have a wii, then you're looking at several hundred dollars, but if you or your kids have one, it is definitly worth the $90. They are still hard to find, though, so if you see one, grab it up! And if you don't like it you can sell it on eBay, people are asking almost twice the retail price for these things!