Yes Fitbit is a great pedometer that gets people to walk more but last time I checked they weren't recording that much data and linking to connected scales is useful but its barely scratching the surface.
One issue with Personal Analytics is we need more data and it needs to be EFFORTLESS to record. The ROI is only high enough when the effort is very low. This is a challenging problem that requires "true innovation". I don't think a tracking app on my mobile phone is going to be the answer.
Another issue is the ability to improve some facet of my life with this data(weight, sleep, etc). Even if I can correlate drinking coffee in the evening is causing me sleep problems unless I can change my habits its not useful information. We need to be able to change our habits and processes based on this data. There are scientific strategies to get people to change habits and simply telling them they need to walk more or eat less do not pass scientific muster. Trigger -> Habit -> Reward. If we need to change Habits we must replace them something. If I need to stop drinking coffee then I need to replace it with something.