Folksonomies - the ad hoc tagging by anyone of anything - sound terribly democratic compared to your top-down authoritarian imposition of taxonomies, but it's easy to see why people are sceptical about them: how can anything useful arise out of something so chaotic?
Del.icio.us is one example of how such folksonomies can be really useful, and here's another (and note the groovy .museum domain - the first time I've seen this):
"Steve” is a collaborative research project exploring the potential for user-generated descriptions of the subjects of works of art to improve access to museum collections and encourage engagement with cultural content. We are a group of volunteers, primarily from art museums, who share a common interest in improving access to our collections. We are concerned about barriers to public access to online museum information. Participation in steve is open to anyone with a contribution to make to developing our collective knowledge, whether they formally represent a museum or not.
Very cool - both in terms of adding metadata to objects, and as far as getting the public involved with art. Indeed, this idea should really be extended to everything - imagine a database of public places that people could tag.
Great idea, then, but why "Steve"?