Clay Shirky has a new essay up about tagging, which he believes is as revolutionary as the Web itself since it casts off the taxonomical pretensions of the professional classifiers and fully realizes the power of the virtual space.
To be sure, rigid categories and elaborate hierarchies do have their place and Shirky notes that they are great in the sciences. Since they have stable entities and experts both producing and consuming them, ontological classification is appropriate for the periodic table or animal classification.
It’s a long essay—19 pages printed—but it’s worth the time.