Definition
Sites whose primary purpose is the cataloguing of material owned by its members (books, DVDs, music), while also building a community of users with that shared interest. Above and beyond the standard cataloguing, users build up a vast quantity of social data around the records, such as reviews, recommendations, ratings and tags.

Examples:

How can libraries use social cataloguing sites?
Adding books onto sites like LibraryThing gives libraries access to the social data and web 2.0 aspects (blog widgets, RSS feeds), which can be used to promote new accessions, and offer more information to readers about the books arriving in the library.

LibraryThing also includes LibraryThing Local, which is a directory of libraries and bookstores which are searchable by location. Adding our library information on to here would be another way of reaching out and giving us more of a presence elsewhere on the web. Many Oxford libraries already have listings, which you can 'claim' if you have a LibraryThing account.

Social OPACs
LibraryThing for Libraries integrates social data into web OPACs, and library management systems increasingly offer social OPACs (such as SOLO), incorporating tags, reviews, recommendations and personalisation etc into their catalogues. This allows users to contribute to the catalogue and add value, without undermining the traditional functions.

OCLC has launched a web 2.0 version of WorldCat, which allows users to add reviews and information to WorldCat records, as well as create and share personalised lists of records. There's not as much participation as LibraryThing so its social data is not as expansive, but it has great potential for use by libraries eg with reading lists, new accessions lists, specific subject lists etc.

Google Books' My Library offers similar functionality.

Further information