Ontology is Overrated: Categories, Links, and Tags

Clay Shirky has gathered in this page two presentations at recent conferences, making the case for unformal, bottom-up, folk-edited categorization of Web resources vs formal ontologies.
What I get from this very clear and intelligent paper is the notion that, in the open Web, efficient semantics are likely to emerge from free tagging, more efficient indeed than those built in pre-defined well-thought ontologies. It goes with the experience of my few past years of development of ontologies and constrained topic maps : very efficient for intranet and corporate environments, they will give poor results on the Web at large.