tagging is collective emergent faceted classification

Something that struck me over the weekend, traditionally faceted classification is against a controlled vocabulary or structured ontology. Products such as del.icio.us and Flickr use tagging to create a similar effect.
The tags act as a nonhierarchical structure to describe attributes that a photo or url possesses, however the facets are emergent from the weight of the tagging. By this I mean that the number of people who use the same tag to describe the same url in del.icio.us then the more the url can be said to express this property. The knowledge space for these tags is also emergent and describes the interest space of the membership.
The del.icio.us popular page gives an indication of the popular pages by numbers of people listing them. There is some interesting analysis of the tags to be done in terms of their usage, by person, by use of same words across people, by looking at how tagging develops with experience. Other things that might be interesting are number of tags used per person, or per topic area. Now to work out how to do the analysis.
UPDATE: I have since, of course realised that I have described a "folksonomy", I was quite tired, so missed the connections my brain was making.