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."
That doesn't account for the times the receiver decrypts your communication and then intentionally makes it public.
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..
