Ben Brooks on personal activity monitors:

What happens though when you are someone that just says: “I want to be more healthy.” That’s not something that can be quantified in steps taken per day, miles walked, stairs climbed, hours slept — yet this is exactly the type of goal the target market for these devices are seeking help with.

I agree to a certain extent. These devices are more about tracking and being consistent, they won’t tell you how to improve. For 99% of people, more exercise would better, so finding out that a person normally takes 3000, steps, and then increasing that to 5000 would certainly make a difference. But if this person drinks 5 extra Cokes as well, that cancels is out.