This shouldn't surprise anybody who has lived in a small town -- when you are in a fish bowl, you manage how you present yourself differently than when you are in a big urban anonymous situation. I choose not to live in small towns, and I choose not have a facebook persona, precisely because I don't want to have to worry this crap. (I think Facebook has already lost its mojo because of these issues, but that is another story.)

Regarding "authenticity": please, give me a break about the "real you". The part inside you that wants to rip off your clothes and tell dirty jokes is no more "real" than the part, also inside you, that maintains your social persona. Without sociality -- and the maintenance of personas and ethics -- you don't exist, period. Even the idea of "authenticity" is given to us, a (rather lame) invention of the 19th Century Romantics, Freud, and the 1960s.

(Edit: Some of the existenstialists would even go so far as to say there is no "real you", and that the anxiety created by this lack of anchoring is one of the most important aspects of the human condition.)