I tend to change my avatar every 2-3 months. Though since May last year they've all been Rainbow Dash, cept it was Fluttershy at first. That RD came on the scene (Favorite pony). I'll just feel they're boring or find a way cooler pic.
I believe before that time my avatars were of Sir Schmoopy (UR), something to do with Nod (C&C) or one of my furry RP characters. That all was so long ago though.