I’ve been using this for about six months, but I think I’m done with it. I like the simple, bare-bones design of the thing, and the very nice Fitbit iOS software, but …

• Battery life is already degrading. When I got it I could go about a week between charges; now it's down to 48 hours.
• Which is made worse by the fact that the plug to the charger (proprietary — I wish it were mini-USB) is delicate. It is very hard to be sure that the device is charging, and even the slightest jar is enough to break the connection. Several times I have plugged in the device, left it to charge overnight, and discovered the next morning that it hadn't charged at all. (The cord is also very short, which means you have to balance the device on top of the plug to keep it charging — if you just let it dangle the connection will break.)
• The iOS software is beautiful, but it has trouble remembering my account — I frequently have to log in, which means finding my password in 1Password, etc.
• Some functions of the device just don't work consistently, especially the sleep tracker. For instance, the last time I wore it all night I checked in the morning to discover that I had slept for 40 minutes around 11pm and then for another half-hour around 4am. In fact, I had slept through the night.