I've owned a lot of "quantified self" style gadgets over the past decade and all they've really done is make me realise that numbers along aren't enough to get me to change my lifestyle. The data is interesting, but it isn't information because it lacks context, and as such it doesn't do anything for you. Seeing a pretty graph that tells you that you've gained some weight might sound helpful and motivating but (for me) it was actually just a little depressing.