This subject comes up quite a bit. From what I've read, the decision is split 50/50. Some say that making your shop more personal with a personal picture will lure the customer in, while others feel that customers will look at the avatars to see exactly what a particular shop sells, or the avatar is intriguing enough to get them to check it out. I'm with the later group. My avatar is my logo/branding. It's on everything that is in and goes out of my shops. My labels are a spin off of it, and I couldn't be happier.
When I see an avatar of a woman with her baby, I immediately assume the shop is selling baby items (not always the case). If I see an avatar with a man and woman from a wedding picture, I assume they sell wedding related products (not always the case). Personally, if people want to get to know me or see the old kisser, I'd direct them to my blog or facebook. Just my 2 cents though.
edited to add: Your avatar told me exactly what you sell. The picture enticed me to click on your shop...