At Computers in Libraries 2010, John Blyberg discussed the shareware software he created that he calls SOPAC, which is based on Drupal. The SOPAC is designed around the concept of a social online catalog. The library's collection is presented online and built around the community, which includes patrons and library staff.
John's library site, http://www.darienlibrary.org/, for Darien Library, is a wonderful example of SOPAC. Some of the features I enjoy the most are the excellent use of community tags and the community created reviews. Library Staff periodically tag books they like with "staff favorites" and the reader's advisor group tags "Meet us on Main Street", so everyone can keep up with what books are being discussed. In addition, John has tied in the sorting ability to circulation counts so that one can sort by most circulated "Popular", or by community review ratings.
The catalog and the community built around it are always integrated on the site: a wonderful example of contemporary attempts to merge community with library collections.