Is ontology overrated?

Clay Shirky has a session at the upcoming March 14-17, 2005 O'Reilly Emerging Technology Conference on the topic "Ontology is Overrated: Links, Tags, and Post-hoc Metadata". He argues that ontology was needed for physical books (the infamous card catalog) simply to keep track of the books, but with modern technology such a catalog is even more difficult to maintain and simply adds little if any value. As he says:

As we have learned from the Web, when data is decoupled from physical presence, it is fluid enough to be grouped differently by different readers, and on different days. The Web's main virtue, in handling data, is to transmute organization from an a priori, content-based judgment to one that can be ad hoc, context-based, socially embedded, and constantly altered. The Web frees us from needing to argue about whether The Book of 5 Rings "is" a business book or a primer on war--it is plainly both, and not only are we freed from making that judgment firmly or in advance, we are freed from needing to make it explicit at all.

He does have some good points, but I still suspect that ontology does have some relevance to the web of the future. It may simply be that ontologies really belong to the realm of active software agents and that ontologies will be used in more of a dynamic matching mode rather than the kind of author-driven static tagging that Shirky argues against. In other words, it would be better to use data mining tools to dynamically classify content, especially since our classification strategies will evolve over time.

So, I think I would retitle the topic as "Ontology: Misused".