My new squeeze bought one for me back in June. I love that "get off your butt" feature and also love the competition we set up between the two of us. Every Tuesday we get an email comparing stats from the previous week. It's fun and quite motivating. I've lost over 15#...maybe closer to 20 (roughly 208 to 190), my resting heart rate is down from 70 to 62, my cardio fitness score is 46, and I've topped 30k steps three times on days with LOTS of hiking. I've always been in relatively decent shape...but I've gotten into much better shape in the last 5 months.
just speculating here...
...I suspect those who say "I don't know why anyone would buy a Fitbit" are of the same mentality as those, who in previous threads, argued with Dr. Bruce asserting that "BMI is a crock of sh**" when they were clinically obese.