No question with the public nature of Social Media, Facebook, Pinterest, Twitter, LinkedIn, MySpace, there is a lot out there about yourself for people to see. So HOW VISIBLE you are with yourself depends on what?
Think first - who are you, and do you want all that revealed, some of it revealed, little of that revealed? Under age 20 people seem like they are complete open books for some reason
Re-evaluate often - If you are kind of a straight person and people cringe at your occasional off color language or humor and tell you, will you change? If you have a blue mouth or lamp shades on your head at parties does Grandma seeing that on Facebook bother you?
Target the audience - finally in crafting what you write, uploading pictures, tweeting, creating a profile or a photo album WHO is the main people finding that on the web? Be good with that. You drinking half a keg of beer while lying on the floor then trying to get that respectable job in the interview down the road, may not be the ticket.