What is the point of this? I thought the point of spamming was to insert links to your website or promote some product. This just looks like random compliments.
Depending on your site's settings, comments display slightly differently from site to site. The basic comment form includes:
Name
Website
Comment
But I still get a lot of spam containing the website field; it seems like the bot is just automatically submitting POST requests with website included. This should be trivial to detect -- is there a plugin that just immediately deletes all of these out of hand before passing them on to an antispam tool?
If it's a bot sending POST requests, there's a high chance a "Website:" field would be filled out. Innocent users will not be able to fill out the field, in the case of a legitimate comment.
Also, many spammers hit the wp-comments-post.php file directly. Since they hit it directly there is no referrer passed like there would be if a POST was sent to it from a page on your site. This page: http://goo.gl/n5VHm on WordPress.com has information on code that can be added to your .htaccess file that will crush bots that POST to wp-comments-post.php with no referrer present.