Art Rhyno has an interesting discussion of using Google Desktop to integrate search of library collections into Google.

This is the biggest part of the appeal of the Google Desktop to me, it brings attention to local content, and in this case, local content can include the library catalogue. The dynamic view of records in the WebDAV mapping creates a small HTML representation of each record, and it is indexed and cached in the same manner as other types of content. [Inadvertent Gifts of the Google Gods]