Apache Solr Search Integration module provides a "More Like This" block that shows related content. Learn more about this feature at http://robshouse.net/blog-post/me-speaking-about-apache-solr-search-drup... - fast forward to minut 16:16 if you want to hear about MLT.
Thank you for your interest. I apologize for any inconvenience this limited access causes. This online guide is now a book called Drupal: The Guide to Planning and Building Websites. The content of the guide is being updated, expanded, and edited. It will include tips for D6 and D7. I hope you will find it useful.
