Go you for posting this.
My dad's going on about it all the time but I still have two myspace accounts (one I never used because I forgot the email) two facebooks (One was completely fake) and three blogs (only one of them gives anything near my personal information).
It's true what you are saying, people have been fired or not even hired because of the content of there myspaces or facebooks, and I once posted something on one of my blogs and then deleted it (it was a chapter of a novel I'm writing, and I didn't want it to get stolen).
However, when I Googled that post title the only thing that came up was that post. Although when I clicked the link it said 'content could not be found' or something like that, you could still see part of the post on google.
So yeah, people should be very aware of what they're doing.
Again, thank you for putting that out there.