A lot. I get bored of my avatars easily and, unlike many people in here, I think changing avatars keeps it fresh and helps people to notice you. (Since it's a nice little conversation starter.)
The one I currently have is a collaboration with a certain someone on the forums. We switched our usual theme around.
My first avatar was one of a group of Pikmin. (Which is probably the longest I ever kept an avatar.) Then my most recognized avatar is my Piplup one which started the Piplup Virus. (Or whatever you want to call it.) And now one of my new(er) themes is K-Pop/Asian chicks!
I remember someone posting a link to a collection of all the avatars each member has ever had. Looking at that list, I was clearly the member who couldn't keep an avatar. 










