How much of your tracking is manual (or intentional, like I heard @accarmichael describe it once) vs. automatic and how do you think that affects what you choose to do with the data?
I'm defining manual tracking as updating a Google Spreadsheet, taking a photo, or writing yourself a note, and automatic tracking as wearing a Fitbit, using a Withings scale, or using RescueTime.
Personally I find that it's much easier to ignore things that I'm tracking automatically because I'm disconnected from the end result--I put on my Zeo every night but I'm not forced to see my long-term data like I would be if I was updating a Google Spreadsheet every day.