Since so many people seemed to be interested, I went ahead and coded up my new Gravatars plugin: Easy Gravatars. It’s designed to be simple to use — just upload and activate. If you want it to be a little harder, you can visit the plugin’s options page to set the size and rating for the gravatars, and even set the location of a default image, and tweak the CSS a little bit.
I’m going to put it in the WordPress Plugin Repository when I get a chance. Once that’s done, I’ll update this post with the new location.
Update, 2007-11-16: The plugin is now in the repository, and you should now be able to see that version 1.1 is available: Easy Gravatars Plugin