I agree that ontologies (as in “library classification systems”) can’t save us, but if you approve of Everything is Miscellaneous, you should also approve of Folksonomies.
If people can decide their own categories or define their own labels, you at least are freed from someone else’s rigid and perhaps outdated knowledge classification scheme.
In some circumstances, it might even work better than ML methods for term extraction from full-text. Consider the case where terminology changes over time (e.g. “AI” -> “Agents”). Folksonomic tagging might allow you to identify an ’80s paper on (what used to be known as) “knowledge representation” as relevant to a “Mobile Agent” application, whereas term-extraction alone might not give you that information.