Most people in the writing world (even in my writing groups) know me as Lauren Ritz. It has just been brought to my attention--well, actually years ago it was brought to my attention--that many people have no idea that's a pseudonym.
Lauren is me when I'm writing, or doing random writing stuff like blog posts and twitter. She's closer to who I really am, at this point.
People have lots of reasons for using a pseudonym, from hiding their identity to splitting genres that are totally different. In my case it was more of a need than a desire, although I've found Lauren convenient since I made the decision.
My "real" name is not quite pick-letters-out-of-a-hat bad, but it's close, and having a name no one can pronounce and no one can spell is death for an author. All that pesky stuff about alphabetizing? Yeah, that.
On the other hand, I've learned that Lauren stands between me and the hard stuff. When I write things that are emotionally hard for the "real" me, she can write them relatively easily where I might break down and start bawling. Or am I mixing my pronouns? :)
Sometimes it's hard to tell where Lauren ends, probably because we are essentially the same person. Still, when I think about being Lauren I find I can write more honestly, even though most people who know Lauren in the real world know us both.