This plugin quite simply lets you know where the users entered your site when they leave a comment. A lot of people who joined the do-follow movement are listed on sites which are a target for comment spammers. To those who suffer comment spam can now find out the page they come from, and block accordingly.
This plugin uses a cookie to track the commenter, so if the user hits the first page first, they will still be tracked.
This plugin is available for download to be used on your WordPress self-hosted installation.