One of the first projects I am working on here at ThinkShout requires full-text search of file attachments. This is accomplished using the Apache Solr Attachments module. We're also using the Facet API module to allow the users to filter their searches based on certain criteria or "facets". The Facet API module provides several useful facets out-of-the-box, such as a filter by Author and by Content Type. One facet that we wanted to enable for the client's users is the ability to filter on the type of file(s) attached to a node. The Facet API module allows a developer to create filter blocks based on fields indexed by Apache Solr Search Integration (or in this case using Acquia Search with Acquia Network Connector).