I got online very early in the history of the net. At the time, I used my real name. As search engines became more powerful, I began to realise that this was a mistake. I'm the only person in the universe with my name, so anyone who searched for me would find things that I didn't necessarily want associated with my name (ah, the follies of youth). I learned very quickly (but not quickly enough, judging by Google results of my name *g*) that I needed to protect my identity online. I stopped doing things I'd be shocked for the 'real' world to know, but realised that just because I wasn't doing anything embarrassing didn't mean everyone I knew needed to know what I was up to online.
So, I came up with a couple of different identities (and accompanying email addresses) to compartmentalize my life. Sometimes, the identities overlap. They're all me; I'm genuine in whatever area I'm engaged in, but my being a Witch isn't relevant to the forum of a game I play nor is the fact that I play that game relevant to those on the forum of a show I enjoy discussing.
Any detective worth their salt could piece together my online identities and link them back to my legal name, so I still try to limit how much information I give in an open setting. I do have a 'private' journal that only a small handful people can read, where I rant about my job in great detail, use my real name, and paint a non-compartmentalized portrait of my life.
Someone I know wasn't so cautious. She kept a public journal where she used her real name, discussed her controversial hobby, mentioned her employer and colleagues by name, and shared truly personal information figuring that she had nothing to hide and who would be interested in her anyway? A copy of her journal wound up in the last place she would have expected and the fallout could be shattering. I hope for her sake that everything blows over with no major repercussions.
"Life's but a walking shadow, a poor player that struts and frets his hour upon the stage and then is heard no more. It is a tale told by an idiot, full of sound and fury, signifying nothing."