is it the form or the function that's the problem?
Activity trackers seem to be like privacy tools -- they appeal to a minority of consumers. And just as it's hard to assess the value of privacy, it's hard to assess the value of activity data. You can certainly measure improved performance by tracking activities; but it's hard to know how that would compare to not tracking the activity and still doing it. In the end, I fear activity tracking is just a hobby that has no real meaning beyond itself.