Since 2008.
I originally had an Aegis Destroyer, then requested some help in getting a good frog avatar.
http://www.escapistmagazine.com/forums/read/18.73740-I-need-help-fixing-my-Frog-avatar-any-artists-out-there#811541
I had 2 offers, both looked similar and I would swap between both of them every month or so as thanks to both of the artists. After my computer crashed, I lost them and had to download it from the site to have it again. It needs some cleaning up, it has become a little distorted after resizing at some point.
To those of you that are constantly changing your avatar, it is really annoying! I tend to not even look at names of a user (I see the avatar first) unless I'm reading their comment or they are they OP. I think sticking with one avatar (or not changing often) helps you stand out. I love that I can be away from the site for a year and come back and still immediately recognize an avatar and remember that person.