My client wanted to be able to search their list manager archives (uses mailman) with Solr. We already had a pretty major investment in Drupal with about 80K PDF files. In the past, each of the different databases were managed by seperate dtSearch indexes. With the new, Drupal system, we are now able to consolidate everything into one master index. With the special ‘faceting’ that is provided within Solr/Drupal, it becomes very easy to drill from the general request down to the specifics.