I recently upgraded to WordPress 2.6, and I was playing with new themes today. One of the things I noticed in the currently active theme is avatar icons next to comment postings. Thinking that was fairly nifty, I went to the WordPress admin panel to set up my icon. No dice; there is no way to set it from there. OK, right-click on the avatar image and check out the URL. The URL points to a site I had never heard of: http://www.gravatar.com/
The premise is nifty. Globally consistent avatar images anytime you post to a Gravatar enabled blog. The gravatar enabled blog generates an image src tag that uses a MD5 hash of the email address you supplied for the account or comment, so that it references your Gravatar image without exposing your email address.
Alas, unless they 'go evil' and start replacing people's avatars with advertising icons, I'm just not sure they'll be able to make enough money to keep afloat. Surely they are using the images served to track people's web-related activities; but is that knowledge really worth serious cash?