A couple months ago I checked to see if anyone had written the exact and obvious words “ontology is underrated” or “ontologies are underrated” in response to Clay Shirky’s somewhat overrated Ontology is Overrated. Nothing, and amazingly, still nothing (according to Google and Yahoo).
I don’t feel up to writing a real Ontology is Underrated essay, not least because I don’t have strong feelings either way, apart from seeing mischaracterization (link only tangentially relevant to subject of this post) put to rest.
Peter Merholz’s Clay Shirky’s Viewpoints are Overrated would be a pretty good start on a definitive Ontology is Underrated.