David Rowan (Wired) writes in his article about why not to post Facebook profiles
2) They make it harder to reinvent yourself
“When you’re young, you make mistakes and you do some stupid stuff,” President Obama warned high-school students in Virginia last September. “Be careful about what you post on Facebook, because in the YouTube age whatever you do will be pulled up later somewhere in your life.” He’s right: anything posted online might come to haunt you permanently, yet all of us need space to grow. As the writer Jaron Lanier said in a recent lecture, if Robert Zimmerman, of small-town Hibbing, Minnesota, had had a Facebook profile, could he really have re-created himself as the New York beatnik Bob Dylan
Hmmm ... I wonder how often people are embarrassed by things they've posted online. I can imagine Facebook having a negative impact on one's career -- for example, if someone were trying to get a job as a teacher in a conservative private school, and their Facebook page had photos of them posing nude to show off their tats. I myself have two separate personas -- the tax lawyer and the farmer. I'm not ashamed of either, but they're each very different from the other.