So I got my FitBit about six months ago and promised I'd come back here and give my impressions after real usage. The verdict, I barely carry it anymore. :(
For the first four or five months I really did keep up with it, then I fell out of the habit during a trip and I just haven't gotten back into it. I still use the weight tracker at least 3 days a week, but I only remembered to recharge my FitBit last week after it being dead for a month.
The issue for me is that their is very little positive reinforcement. I don't have friends to share data with on the site. And once you know what your averages are, well they don't change much. And since I'm not trying to use it to get into better shape, the values really don't mean much to me. I like tracking my weight, but I don't need a pedometer for that.
Might be really cool if it was integrated into a life dashboard or some such, but as it stands I'm sad to say I don't find it nearly as compelling as I'd hoped. Which is too bad, because I was pretty pysched about it.