A friend of mine in Seattle was fired from his job because of what he posted on his personal blog and MySpace [about disliking his boss, I think]. It was a really high profile case because it was the first publicized one of it's kind. The story got tons of media attention for the freedom of speech issue. He did not get his job back.
There are also stories of universities and corporations alike checking on candidates for scholarships and jobs and finding things that led them to make other choices.
The internet is rife with potential pitfalls when it comes to how much you share of yourself. There are profiles I've seen on various networking sites that I just KNOW the user is going to beat him or herself up for later...
I think Lily's Grandmother said it best