Personally, I don't like them very much. In some places (gaming sites, Facebook, etc.), I can see it. But on a professional site, like Webmaster World, I think it's distracting and makes things look less professional.
Plus there's the issue of people using copyrighted images.
Allowing an avatar or other picture on the user profile page? That I wouldn't mind seeing. But the same image next to each post? No, I am not for that.