Where do I draw the line between private and public?

Where do I draw my lines between what I reveal in public, and what I keep private?
In the age of Big Brother and Paris Hilton (the girl not the hotel), is there anything that is an unacceptable part of public discourse?
Is there anything that I should not reveal?
What are the dangers of being too public?
Is it more dangerous to be caught somewhere in the middle between anonymity and celebrity?
More dangerous than at either of the ends?
How can I make any difference to anything without being public?
Is there anybody out there?