Comment on WordPress Gravatars by Mark.
Right now there is a little white/grey square to the left of the recent comment in the widget side panel.
What if this was a gravatar of the commenters?
Hence, you attract people into the conversation as people on the web are attracted to faces. That is what rocketed Facebook, faces.
It is programmed into humans though evolution to respond to a face and deeply coded in our brain as survial depended on it. Therefore it leverages this brain code.
I would imagine if this was developed you would see a greater click rate and community without having to create profile pages.
I know it would be a pain to fit the images in as they would be the size of a favicon. But it is an idea, or expand the size to the Gravatar is above the comment.
Users could also create a set of default Gravatar that are congruent with the theme of the site. So if someone had a website about accounting. They could make Dilbert looking default Gravatars in Gimp or paint.net; when actual users do not have one. This would be much like how you ramped up your ‘related posts’ with default panda images.