Web 2.0 theorists argue that Internet technologies now allow us to harness the 'Wisdom of the Crowd' in unprecedented ways. Successful online experiments such as Wikipedia demonstrate that the collective knowledge of millions of users can produce reference works that are more comprehensive than traditional reference sources produced by a small group of experts. Similarly, "folksonomies," which use the judgment of the crowd to organize documents, have worked extremely well on popular Web 2.0 sites such as Flickr , del.icio.ous, and LibraryThing. By collecting and analyzing the private descriptions ? the tags ? that users add to their own photos, URLs, and books, these sites generate valuable metadata about public documents and resources.

Traditional library OPACs lack mechanisms for collecting the knowledge of library patrons. The classification schemes used to organize library collections rely on the expertise of a small group of specialists with detailed knowledge of the Dewey Decimal system, the Library of Congress classification system and the Library of Congress subject headings. Although this system works well as far as it goes, a Library 2.0 catalog that could generate additional metadata from the wisdom of library patrons would enhance the value of the OPAC. An library catalog that could point users to recommended titles in the collection based on the reading habits and descriptions of their fellow patrons would be a great benefit to many readers.