I'm definitely guilty of signing with only my forum name (just went back to my emails with David and sure enough--all signed "ZENGHOST").
My first reason for doing it is that I hate my real name--and my friends don't even use my real name so I try not to use it too much. My second reason is that my forum name is my identifier if I am emailing someone I've met over the forums. If I email someone with my real name, it'll mean nothing to them, but if I say this is "ZENGHOST," then at least they'll know who they're talking to. In fact, I don't like it when someone contacts me about a sale/trade and does not tell me their forum name. If someone I'm communicating/dealing with asks me my real name then I have no problem sharing it with them--especially if I want to buy something from them. I do not post my real name on the forums, though--I'm a bit paranoid about that sort of thing. My name turns up in too many web searches as it is. I sometimes even have people send stuff to "ZENGHOST" when I buy things from them.
David, I'll be sure to include my real name in our next communication. Have a good one.