Best advice I ever heard (and it came from an ex-Facebook employee), "treat communication ("private" & "public") on all services, including Gmail, Facebook, and Tumblr, like a million people are listening."
There's a deep wisdom to the idea that one ought not put into words that which they wouldn't want the world to see... Once it's out of your head, your ability to control it diminishes if not outright vanishes... Just say'n is all..
It has yet to hurt me.