I'll change mine once I have a quilt or quilted project finished. Right now, my avatar is a piece of my beginner class project. Before that, it was a drawing of a sampler quilt block I was having problems with. I don't know that I plan to change it at regular intervals. It'll be more as the mood hits me or I have something better or more "me" to use.
AtHomeSewing, yours is beautiful! I'd miss that if you changed it.