Names have power. Your name, handle, nickname, call sign, userid, email address, IM ID, identifies you. There's a reason we call it an ID.
A name you choose for yourself has even more oomph. My mother named me Vicki, but; I choose to call myself Vicki. I don't have a nickname. (When it comes to choosing an online identity, e.g. for a Second Life avatar, I'm stymied.)
My email ID is vlb. I've been using it for so long, and am so comfortable with it, that I chafe at companies that assign me something else. When I can, I request an alias. When I can't... well, I didn't work there for very long.