I dunno about data, but I refreshed my phone last week from scratch because of high Android OS use, and now it's been stuck on 74% for a while now. I wish there was a more accurate way to see what's using the AOS.
The app "System Info" will do that. After you install it, check out their website (it's listed on their Market page). They also offer Logcat. System Info is great though. Anytime I am having any issues, I install it and look at system activity.
Good luck.