Now you can learn more about WordPress.com commenters simply by moving your mouse over their Gravatar image.
The new feature, called Gravatar Hovercards, will display information from a user’s Gravatar profile, including their name, bio, pictures, links and contact information for social sites like Twitter and Facebook. The feature is enabled by default on WordPress.com blogs, though it can be disabled by going to Settings > Discussions > Avatar in the administration panel.
According to a comment by Beau Lebens, a plugin will be released for users of self-hosted WordPress installations that will enable Gravatar “extras”, including Hovercards. Until then, a hack has been released for enabling the feature on self-hosted blogs.