I'm not going to bother going through what the Fitbit does and doesn't do in terms of features... if you want to know that, you can go read their own website for details. I'm going to share some of my thoughts on actually using the thing and what it's like to live with... I think that'll be more helpful.
Actually wearing the thing is something to get used to. I initially started using the belt clip with it and actually attaching it to my belt. That works well enough and all but I had a couple concerns. The first being that I worried that if I hit it just right on something, the device would pop out of the clip and I'd lose it. It never actually happened, but it could have. Secondly it felt like it stuck out farther than I'd like while in the clip - which led to more concern for point number 1.
I find myself just attaching it to my pocket now. If I'm wearing jeans, the change pocket (for guys anyway) is perfect. If I'm wearing something else, it depends on what it is and how many pockets... but typically it's just attached with itself and no belt clip. Oh... and the wireless syncing is awesome. It's nice to not have to dock it every night to transfer data. I'm still learning how long the battery lasts though - no real feedback on that.
One thing I found while racing the other day is that if I tightened my seat belt like I normally do (basically engaging the safety stop on purpose to lock me in place) it ended up accidentally holding the activity button down and starting a new activity. Not a big deal, but it certainly opened my eyes to the possibility of something unintentionally activating it.
As I have probably mentioned in the past when looking into this thing, I was really looking forward to the sleep information. Having used it at bedtime for the last week, I have a couple thoughts. I initially thought the little wristband thing might be a bit annoying. I'm not used to sleeping with anything on but a pair of shorts. Surprisingly it doesn't really bother me. It's relatively unobtrusive and fairly comfortable. Turns out to be no big deal.
I also realized that the sleep data isn't exactly what I had hoped. I mean, I think the data is what I expected it to be but I guess I never really thought about what I could do with it - which I think is nothing. I can look at it and think "ya, I slept like crap last night" ... but that's about it. I'll have to look into what the stuff means and if there is anything I can do about it.
Overall though, I'm pretty happy with it. I have a job such that I typically walk a lot and it's been kind of a curiosity for a while to know how much I'm really moving around all day. Plus I was never really one to track my food/calorie intake - but now that I have something to compare that info to, I find myself taking the time to enter in my food each day. It's kind of annoying and sometimes I have to estimate as best I can, but it is good info to have. As you can imagine, if calories burned > calories taken in, that's a good thing.
It's only been a week, of course, but so far so good.