There is one open-source project that manages synchronizing a fitbit to their service. Apparently, one used to be able to get data from listening to this communication, but they now encrypt all data coming off of the device.

I got a Jawbone Up24 for my birthday, which seems to be a similar device. I'll see how easy or difficult it is to get data off of that. (I think it's designed to sync via bluetooth directly to a smartphone, which then syncs to their service, so there might be some more wiggle room on communicating to the device).