No doubt that Stefan Decker and Tom Gruber are the most influental persons in the involving semantic social web. Both are working on a unified view on folksonomies & ontologies, practical as well as formalistic aspects of the web and develop things like the “social semantic desktop” or “tag ontologies”.
Tom Gruber´s presentation at ISWC 06 “Where the Social Web Meets the Semantic Web” can be watched at videolectures.net: In one of the main parts of his talk he will state the question: “How can we put all these tagclouds out there together?”
Definitively an important question…
The accepted term for this phenomena is sociosemantic web and it’s been examined in considerable technical depth to achieve progress in tag ontologies and data fusion.
One of the useful insights of sociosemantic web work is that categories are useful only to establish filters while namespaces are useful only to establish limits or governance from a particular point of view. A useful category lists pages that may all be of interest in a particular phase or a process, most typically a learning process. A useful namespace is commenting on the parallel page in the main namespace.
Categories are thus a subset of tags, but namespaces are orthogonal, because the point of a category is to shape people’s language to a particular taxonomy, but the point of a namespace is to differentiate who or what faction is speaking or asserting. Categories should actually be renamed as “pivot” or “facet” to reflect that they are almost always multiply applied, since each purpose a database has means a different hierarchy of categories.