The Wall Street Journal has an article today with yet more examples of why you need to think very carefully about what you do and say on the internet. Social networking sites make keeping in touch with many far-flung friends easy and fun - but you might as well be standing on stage in front of all the TV networks at once with a microphone for all the privacy you can expect.
When you talk to groups of people at once on social sites, you should expect that everyone, including your mother, your spouse and your boss, can see what you say. There is little to no boundary between public and private on these sites. And if you are not tech savvy enough to understand the privacy settings, then act as if you have no privacy at all. Say only what you would say if you knew that everyone in the world were listening.