I have been doing this for many years now. I am "spiffytech" everywhere on the Internet, and that identity has extended to my physical relationships. In my college LUG, everyone knew me pretty much exclusively by my handle. This topic once came up there. I asked a friend who I'd known for four years if he actually knew my real name, and he had to stop and think for several minutes before he could respond with my name. Another friend I'd known for about as long said the only reason he knew my name at all was because it's in the "From" line in my emails.

Despite the fact that I never operate online under my given name, the fact that my username is tightly tied to my identity and reputation prevents me from employing it as a shield of anonymity to hide behind while I lob uncivil or disrespectful remarks at other Netizens. I don't generally feel tempted to do anyway, but I can't say how much of that is due to my consistent use of my username.