There is a great debate going on (most interesting between C. Shirky and L. Rosenfeld) about “the folk’s” new way to escape the librarians’ sophisticated cataloguing rules. (And parallels can be seen in “2nd party metadata” for eLearning, see slide 12 of this presentation, and in the “disdain for hegemonic practices” with Wikipedia, see D. Boyd on elitism.) Uncontrolled tags from a flat address space as in del.icio.us, or a predefined taxonomy with hierarchical relationships (BT, Broader Term), frequently with an “Other” category which balloons out — which option is the superior one?
I think it is not about superior or inferior choices. It is about deep-seated preferences that cannot be debated, because they are in fact two opposite cognitive styles. One cannot force somebody to use hierarchical “broader term” relationships when s/he has a deep aversion against such hierarchies. And you can’t force someone else’s brain to find tricky search term chains who prefers browsing a tree and leveraging the built-in cross reference management of relatedness heritage and concept kinship.
Knowledge management needs to accommodate both styles for both types of classifiers and visitors. I wonder if somebody from the LIS crowd comes up with tags like delicious/tag/ddc57xyy to simply bookmark the uncontrolled tags delicious/tag/squirrel(s) under their Dewey decimal number….