The FitBit Activity Tracker (on the website, Android application, and I would presume the iPhone application as well) lets you log various activities so you can track and share them with your friends. You can explicitly log things like running, using a treadmill or elliptical, or other activities that would also cause the device to count steps and miles. The device (and the website) also track your calories burned based on your profile, and when you track activities, it also estimates the calories burned based on the type, duration, and other parameters of the activity.
I've been trying to determine how exactly FitBit uses the activity tracker data. Does it convert miles run to steps (meaning wearing my FitBit when tracking a treadmill activity would cause double counting)? Or perhaps is the device smart enough, based on the start time of the activity, to not double count? Or are the things like distance, time, and calories burned in the activity not totaled with your device data?
I'm mainly concerned with the things tracked by the device: steps, flights of stairs, miles, and calories burned. At the end of the day, I'd like at least a reasonable estimate of these things.
I couldn't find anything in the FitBit FAQs as to what is recommended, nor many discussions on how others deal with this.