My problem with fb and the reason I don't use it is simple: principal. I understand the model, and oblige with google (though not g+ as it is pretty quiet in my neck of the woods). But to not only give them the value of my data but also have them go around changing things like registered email without so much as a heads up is a slap in the face. It's like a conceited bus monitor that just goes ahead and "does what's best for me". I'm an adult; I know what email address I prefer to use.
Not only that, but the utter lack of transparency is concerning to say the least. There is this monstrous set of data--PII--that this company holds and who's to say the bus monitor doesn't all of a sudden decide that's it's best for me if they provide this data to Experien. Or to the justice dept.
The real problem is that people are addicted to distraction. Fb offers this droves. So much so that not only are people more than willing to hand over their data, they are willing to hand it over to someone who thinks you don't even deserve to know when they make sweeping changes to which parts of that data are displayed to the world.
/rant