I've used regular pedometers in the past and once I heard about the Fitbit, probably a year before it was released, I was extremely interested in getting one.
The Fitbit uses a technology similar to what you find in a Nintendo Wii to track how many steps you take. Once you are in range of the charging station, which also doubles as a receiver for grabbing the number of steps you've taken from the Fitbit as well as information on how much battery charge is left. The data is then uploaded to Fitbit's own site, where it keeps track of your steps and determines the number of calories you've burned. Additionally, the Fitbit site can be used to also track your calorie intake and has a database of a number of foods. For what it doesn't have, you can enter manually and have it available for you to use in the future. If it is something you eat pretty often, you can mark it as a favorite and have it available on a side menu instead of having to search for it each time. You can also enter activities such as running and bicycling or select an activity from their database. The site also indicates how much power is left in your Fitbit and can be used to track your weight, mood, and various other indicators that may or may not be important to you. The Fitbit site can be used for free without the purchase of a Fitbit and there is also a premium version of the site where you can track more data, but I do not use it.
The Fitbit can also be used to track your sleep. Included is a cloth wrist wrap with velcro that contains a sleeve for the Fitbit. When put into sleep mode, the Fitbit then tracks how restful your sleep is. I used this functionality only once. I don't care for having something on my wrist while I am trying to sleep and the Fitbit eventually fell out of the sleeve. I usually have a good, deep sleep so this information is not important to me.
I found the Fitbit accurate, reporting the same amount of steps that I normally got with a regular pedometer. I don't wear it when riding a stationary bike, lifting weights, or working out with a kettlebell (which, sadly, is not in Fitbit's activity database) and instead keep track of how long I did the activity, and in the case of the stationary bike, what distance I went. The holster you can place the Fitbit in and attach to a belt (or some other kind of clothing) works well, though can be annoying when it rubs against skin.
Be wary of using the Fitbit site to monitor how much battery charge is left in the Fitbit. It records full for a bit after fully charging the Fitbit, but then tends to stay at a status of high, even when it may not reflect reality. I had one morning where the Fitbit site indicated a high battery charge status, but the Fitbit ended running out of power 5 hours later. The Fitbit runs for about 5 days on a full charge, so I would expect a status of medium about 2.5 days later and a status of low when there is about 1 day left. As a further example, the Fitbit site recorded a high battery charge status, but when I plugged the Fitbit into the charging station, the Fitbit indicator (which can also show steps when you push the Fitbit's button) showed 1 bar of battery power left. I'll end up putting a calendar reminder every 5 days to charge the Fitbit.
Overall, I am pleased with the Fitbit and look forward to using it as a weapon in the battle against the bulge.