For some time I use microformats on my contact page. Some days ago had the idea why not use microformats for comments to add hCard markup to the comment entries.

So first I had to replace <?php comment_author_link(); ?> with <a href="<?php comment_author_url() ?>"><?php comment_author() ?></a> in the WordPress template. Finally I added some microformats code: <span class="author vcard"><a class="fn url" href="<?php comment_author_url() ?>"><?php comment_author() ?></a></span>.