I've been wearing the FitBit Alta for a little over a week. The sleep tracking has been interesting. It looks like i usually sleep pretty well - I just need to work on consistent sleep/awake times.
I'm nowhere near the AHA general guidelines for activity, though. They recommend 5 miles, 10,000 steps and 30 minutes of real activity. I get 4-5,000 steps and about 2.5 miles in and 15-20 minutes of activity.
I'm going to start walking at lunch. And I may skip or tone down the meal itself. The FitBit will track weight (if your enter it each morning) and nag for a goal. I'd like to lose at least 10 pounds.
So, so far, I'm liking the little gadget. And it has really good battery life. I wore it 24 hours a day (except in the shower) for 9 days before it complained that it wanted more electrons.