It think about 3 months into joining when I finally figured out how to do it. I searched for something I thought looked unique that no one else had. Later I found out that someone else uses the same Avatar, but he doesnt post as much.
I never bothered to change it because I hate it when members change Avatars. (with the acception of Dolfette, or any female that uses their own pic of themselves) My eye gets trained to see the pic when I scan the page. And I like to identify members by their Avatar pic. There are members whos posts/ threads I enjoy, and others I'd rather skip over.
My favorite comment I got for it was in the thread about renaming the Avatar in the jokes section. Someone called it "an Egyptian cockring". I thought that was the funniest out of all of them.