I came across an interesting study of del.icio.us, by Ulises Ali Mejias: Bookmark, Classify and Share: A mini-ethnography of social practices in a distributed classification community. One conclusion that particularly matches my own observations of "classification culture":

As the findings of this preliminary and limited study show, it is hard for people to make the initial conceptual shift from traditional forms of classification (using fixed taxonomies) to distributed classification schemes (using flexible taxonomies). The freedom to define individual and social structures of classification emergently can be perceived as chaotic, lacking rigor and utility. However, the more comfortable users become with a system’s features, the more aware they become of the benefits of distributed classification, and the more aware they also become of working within its limitations.

One of my main interests over the years has been: what does it take, from a technology perspective, and from a cultural perspective, to create a great interface between centralized classification and decentralized classification? What does it take to create a context in which classification "systems" can evolve from flexible / decentralized to fixed / centralized, and then to flexible again, and then to fixed again, etc.

(And, all that in a context where multiple classification schemes co-exist—including ones that may even seem to contradict each other.)