I generally like to imagine that we are all in some metaphysical land of swirly colors and random text falling down and each avatar is present and talking if they are capable. I occasionally imagine them talking directly to me, even when they are not responding to me. That, or I try to imagine the individual (or an individual because I know nothing about 99% of you) typing their response.
I also tend to identify people primarily through their avatar. I hate it when people who post a lot change their avatar because I start thinking about the guy who had that one avatar and then he has posted, but just has a different avatar.
All this and I yet I never add my own. I find it hard to pin down one aspect of my personality that I want to identify with enough that I want to make it represent me. I'm the kind of person who like wearing shirts without word on them because I don't want people reducing me down to just what my shirt says.