I love my Fitbit. I love wearing it, and seeing that I'll have X steps and saying 'self, walk 1000 more steps before you...' and then I'll do it, and burn more. I like having it as a motivational tool.
I used to have a BodyBugg and I liked it, and the Fitbit records a similar burn, but the BB was $7 a month to look at my progress online, while the Fitbit is free. I'm liking free much more, lol.
I can't think of any negatives. I had a software issue with my first one, and I emailed customer service and they emailed me back on a holiday weekend the same day, and my issue was resolved (they sent me a new one) no charge, and with very little effort on my part. I have nothing but praises for them.
The website is easy to use and the app is too.