I started out with a very neutral picture of a plant. Then I read that if you want to get your Google adsense account approved you should have a picture on your Google account, and on your website(s) (this was an opinion I read somewhere, it may or may not be correct). I changed to a slightly manipulated (posterized) picture of myself. After reading your post I'm going back to an avatar. I think there is a lot to be said for reading for content, like one of the other commenters mentioned. People have unconscious biases against gender, ethnicity, age and general looks. The avatar helps readers get past the physical barriers, and may get them to engage in an interaction (reading, commenting) with someone they might not have considered communicating with before.
When I was in 9th grade, I drew a picture on my desk at school, of an extraterrestrial. On the next day, someone else had added to the picture, and written a sentence about these extraterrestrials. I added to that, and to the story, and for a few weeks I enjoyed a completely uninhibited exchange with whomever was sharing my desk and lack of attention to the teacher. Soon I found out that the other writer was the school nerd, teased by most. I remember how disappointed I was, and that I wished I had not found out. Once we came face to face there didn't seem to be much to say or write anymore. We had lost the camaraderie of sharing our minds. I'm not in 9th grade anymore, but I think the idea is similar. An avatar helps to achieve this sharing of part of oneself, with less prejudice.
I hope you like my new "do" 