The avatar is definitely the first thing I notice about a user, and I think it's the same for most others, but if I really remember a user, then I remember their avatar, their name, and to some degree what they're written, their post count, and their mod history. I'm an internet creep.
I feel almost like the odd one out here. Yes, I remember a lot of your avatars, but I remember your username if you post a lot and/or are a memorable (whether in a good or bad way) poster.
EDIT: Also, in real life, I remember people's names pretty well but I always have this little fear that I'll attach the wrong name to the wrong face. It's not an entirely unfounded fear, but it also isn't a common occurrence.
I assume most people go by avatar. When I met Pascual IRL, he noticed me by my GB shirt and came up to me and I already knew what he looked like from his videos and stuff but I told him my name and avatar and said he didn't recognise me for not being a girl with blue hair :P
Also, in real life, I remember people's names pretty well but I always have this little fear that I'll attach the wrong name to the wrong face.
I don't have that fear, mainly because I identify people by face so much that I don't ever remember a person's name. I have reverse prosopagnosia, it seems.
never changed my picture, but Kermit dose where a hat for Christmas. Also I was seriously considering getting a pin with the Kermit picture on it for pax, but I didnt.
Oh man. If I ever go to a PAX I'd probably just have to cosplay as Pimp Suit Rich Gallup.