I had a conversation with my boss a while back about Facebook. He is totally against facebooking because he said he lets people into your personal life too much. My stance was that you have to know how to control your online identity. Yes, everyone has access to it... even if you using the various privacy options that Facebook and other social networking sites have, there are ways around it.
Example: you set it to "friends only" but what if your "friend" shows someone, and that someone opens their mouth about something they saw on your page... its out in the open now.
So you have to be smart about what you put out there... from a Journalism/Public Relations standpoint, Facebook can me a great networking tool. There are people in the building(s) that I work in that I would never talk to... we'd just send each other work-related e-mails. But now on facebook I can get to know them differently and then make a human connection with them when I see them at work. It alleviates the pressure of work and enriches your professional relationships.
Along with that, it allows you to reconnect with people from your past and helps you rebuild bad connections.
I guess I'm just saying that people need to be smart about the way they use their Facebook. First of all..don't just add the whole world... add people that will increase your social capital and strengthen your bridges. Secondly, don't put stuff out there that is way too personal. Once one set of eyes lands on it, its free game to the rest of the world... and you will have no one to blame but yourself.
That is all...