I thought about this but for me I think a nickname on its own conveys an expectation that it should mean something to me, whereas a real name doesn't - I can just think do I know him/her or not. I remember someone after an event telling me about some exploits which involved "nickname x" (a prolific audaxer) but at the time I had no idea who it was. The nickname meant nothing to me and so it seemed rather cliquey, and made me feel that I was a real outsider as I probably should know who he was.
I think the combination of both real and nickname can be OK - so using Cudzo's example "Rob Norris (known to his audax friends as Gasbear)", or some similar wording, would be fine for me and would enable me potentially to associate the two names for future reference.
As is often the case, context and specific wording is key, rather than hard and fast rules like "no nicknames" - but beware of potential alienation if not done in the right way.
A few years ago I was visiting friends in Belgium. We had a lovely evening of Beer and Frites, and I ended up sleeping on one of the friends sofas.
I woke up with a hangover to discover an old woman offering me a coffee. Turns out it was the mother of my friend. Through the fog of an early morning (I am not a morning person), while drinking coffee, I am asked by this old Belgian woman with very broken English. "How do you know Peter?"
"Who's peter?" I respond.
Because these were friends I had met online, I know this person by an entirely different name. We use our online nicknames in person. Depending on the name someone uses for me, you can tell how long they've known me (my nickname has changed over the years).
There is some belief that "Real names" are important, critical even. But the reality is, the name you know someone by is all that matters. A lot of you know me as Quixoticgeek. I do actually respond to that in real life. I receive mail addressed to it. I also respond to Katje. Perhaps it's being part of Gen X that grew up on the internet, but I really don't see any reason to insist on real names. There is a YACF member who I've known since university days. Approaching 20 years now. I only learnt their last name in the last year or two. I've always known them by just their first name only.
We often see people talk about being anonymous online, we see various attempts by social networks to insist on real names only. And they fail. Because that's not how things work. A lot of people use different names to their "Real names" whether it's shortened (i.e. Ben rather than Benjamin), or a nickname the reasons for which may have been lost in the dim distance past. The reality is, insisting on real names for everything is an out dated idea.
J