Volrath's point about how your avatar effects how others perceive you got me thinking...
I...kind of perceive myself on a site based on my own avatar. It's more like, when I go back and read one of my own posts, sometimes it seems "off" because...it doesn't "match" my avatar!
For instance, sometimes it feels weird to share some of my weirder ideas on this site, because my avatar is a cool, badass robot. Well, if my weird ideas are about robots, lasers, or aliens, it sort of fits. But it almost feels weird to talk about magical girls, genderbender shenanigans, or puppies...with my cool gun-toting robot avatar. And I've used all of those things as avatars on other sites! (actually, can't think I've ever used a puppy as an avatar, that needs to be corrected!)
It's like I bring out different aspects, and mildly suppress other aspects, of my personality based on my avatar.