TALO eGroup member Tony Lorriman posted a link to a pretty good article by Clay Shirky called Ontology is Over Rated. Clay gives an enjoyable, and what I think to be a strong argument why traditional library cataloguing is no good for dealing with digital content in the International Network. Clay's article gives some good insight into the history and emerging popularity of social tagging, or folksonomies for "cataloguing" the Internet.
It would be useful to view Jon Udell's screencast Language Evolution with De.licio.us before and/or after reading Clay's article as it is an excellent demonstration on how it is working in the world now.
Steven Downes on the other hand, argued against social tagging in his recent presentation on Community Blogging at Northern Voice.
Viewing, reading and listening to the resources listed here should give you a pretty solid introduction to the new trend with some very interesting potential.