Clay Shirky's weighed in on the freetagging vs structured taxonomies debate:

I, on the other hand, am of the unreasonable view that classification schemes are going to be largely displaced by tagging for the same reasons that search has largely displaced directories for finding things, namely that distributed intelligence, for all its faults, tends to beat the work of a professional class when dealing with large, dynamic systems.

See the rest of his post on You’re It! a blog on tagging. Notably, Shirky categorized his post under "uncategorized" :)