Seth Ladd's post about improving MT with DMOZ uris really has me thinking about cateogory sets again. The fact that the rdf representing the DMOZ tree is 51.8M (gzipped) says a lot about the need for communities to agree on standard categories for blog entries.

I can see an individual blogger subscribing to category sets published by several different communities. These categories would be used, as Seth envisions, in the MT entry interface, and represented in the rss data by dc:subject. Community aggregators such as PlanetRDF could then be pinged only with stories appertaining to its published category set (or the reverse).