I personally used to go through avatars pretty regularly on this site. Below are all the avatars I used in the period between September 2011 and July 2013. I always looked for something I could keep as a regular avatar but at the end of the day none of them felt right. I thought I finally had something with Lichtenstein's Half Face with Collar and I was able to slightly tweak it for Halloween and Christmas but after that I eventually got tired of looking at it and wanted something new.
However, in July of 2013, after the hype of E3 and the "next gen" consoles had died down I came to the realization that Nintendo had the best games coming out that year and their future was looking much more interesting. I decided it was time for a new avatar, but this time I was in the mood for something Nintendo related. Not only that, but I wanted something that I could easily tweak so that I could slightly modify it if I got bored but still keep the core image the same. I also wanted it to be orange because orange is an awesome color. With Pokemon X and Y coming soon I decided I would look for an awesome Charizard picture since he is the best Pokeman and ended up finding this snazzy looking one on Society Six by David Thomas. Depending on how you define "same avatar" I have been using the same one for either one year or less than a month.
So how long have you duders used the same avatar? How often do you change it and why?