It's much easier to remember nick/screen/usernames, than regular human names. I was reading something a real-life friend of mine wrote (though, I don't see her that often - this may have some relevance), and she referred to herself in the text using her name. It took me a bit to recall that that's her real name. On the other hand, because she has a unique nickname, like most of my friends, I would associate/connect it with her right away.
Same goes for most of my friends, as long as the nicknames are actually unique. Having two friends - a guy and a girl - both with online nicknames "Murzilka" is at times confusing :)
So what we should do is create a database, and allow people to name their children with strictly unique names - no duplicates.
I wonder if many kids will be named "XsweetieX5234342" and "BaDbOy02394851"...