I tend to change my avvie to fit the theme of the game, at least to an extent. (For instance, for I started with a Hermione/books avatar for Lari's game, a Pirates of the Carribean one for Brinn's, the gloves for when I helped co-mod Mnemo's, etc.) Also, if I'm killed I'll switch to one of my Firefly icons, and sometimes I'll put up an icon that tells people in the game what I am (but that's only if I'm being a
complete whackjob and has only happened once or twice that I remember.) My icon normally carries over from the previous game until I change it for a new, or forget to change it at all, and I don't have a default because....well, I've not found one I like enough yet, to be honest. (Though I am a bit fond of my Hamlet with a happy ending icon that I made a while back.)
And Lommie, that icon is you to me. I recognize you with different ones, but when I see that picture I automatically know it's you.