Mike and I have had the wii for a while now (Eric was kind enough to send us one when they got lucky purchasing two) and we haven't used it much. Unfortunately most of the games haven't lived up to the hype of the wii, and one of our all time favorite game franchise, Metroid Prime, seemed a bit disappointing with the wii. Once we bought the xbox 360 there was no contest and the wii just gathered dust.
When wii fit came out, I was curious about the effectiveness of the game but couldn't find a copy anywhere (without the inflated price of ebay). After a couple of gentle nudges from Mike I decided to just sell our wii since we just weren't using it and the demand for wii consoles was still high. Before I sold the wii I was able to borrow a friend's copy of wii fit.
The wii fit focuses on aerobics, yoga, balance games, and strength training. The aerobics are interesting but don't last long enough for a real workout. The balance games are fun and help you to control your sense of balance but I think the most useful are the yoga and strength exercises. The yoga exercises help me stretch and strengthen a very stiff out-of-shape body while learning to balance myself correctly. The strength exercises uses your own body to tone and train. After the first day of wii fit, I found myself with some sore muscles and a profound respect for those who can be flexible enough to do some of those yoga poses.
I'm using the wii fit as a supplement to the aerobics and weight-lifting mostly to improve my balance, stretching, and muscles. However one surprising benefit of the wii fit has been to increase my focus on what I'm doing when working out. Since the fit uses a balance board, you have to be aware of your form, position, and balance when doing the various exercises. I've used this ability while weight-lifting and realized that I haven't been doing a lot of exercises correctly. Notably because I can feel the right muscles working now and I'm also rather sore this evening although my weight-lifting regime hasn't changed at all.
So I think we're now going to keep the wii and continue (hopefully) to use the wii fit to help us get into better shape. The fit is what you make of it. You can do a half-assed job and think the game is stupid or you can really work at it and get a pretty good workout. Granted it's not a replacement for regular aerobics and strength training but it is quite good as a beginning or supplement.