Without editorial control, social tagging (metadata), making up subject keywords, is doomed to fail. Rogue marketers will corrupt the process to meet their ends, like what has happened with spam blogs. Automated indexes cannot differentiate between legitimate blogs and spam, see wikipedia.

I love the enthusiasm of librarians towards social tagging, but the system needs editorial control or oversight to prevent abuse. I've never found Flickr tags to be of any use. del.icio.us or del.icio.us is so over-rated. What we need is an open source version of the LC Subject Classification, like Linux, many developers, each upgrade needs editorial oversight.