Here it is a new WordPress plugin that auto-detects and shows in real-time the Gravatar image when users are filling the comment form.
Fork of the Gravatar Box plugin by Otto, based on the MooTools javascript framework (instead of jQuery), with a nice fading effect.
It’s easy to use and configure, further and more easily customizable options will be available in a near future release.
Please visit the plugin page on WordPress for more details.