I've had mine for over 4 months - yesterday was my 4 month anniversary with it. So far I've lost 13 pounds, and gotten my BMI below the recommended 22!

And yesterday was my best BMI ever - 21.39!
This is a big deal to me because my goal (dream!) weight would only be to lose 2 more pounds. That would be back to my college weight 20 years ago, so I'm happy with what I've done so far. But it's definitely getting harder - I lost the first 10 pounds in a little over a month, and the last 3 have taken about a month each!
Honestly though, I haven't used it much for the activities, but more as a daily weigh-in and reminder. I know that if I eat junk, that the next day it will show up and the Wii will end up consoling me ("it's okay, keep trying!). Trying to reach my weight loss goals (right now only 1/2 pound every 2 weeks) keeps me motivated and excited when I do reach them!
I am thinking though, that as the weather gets bad that I may try using it more. Right now it's just been too nice out not to take advantage of running or biking, but trust me - here in Green Bay, that's not going to last long! I definitely recommend it if you think you could stick with it, but no one else in my family has.
One thing to remember when you do get it is that the activities start out really easy. So don't do the easiest level of things and assume you'll never get anything out of them. If you're already in fairly good shape, most stuff will be too easy for you at the start, but they do get tougher. Except the balance games for me - apparently I have NO sense of balance.

I play the soccer game and do my best to score above zero. My kids do it (and they hardly ever play it) and score over 200! I do enjoy the strength training - especially the abdominal workouts - and can hold my own against my kids or my "trainer"!
Good luck!