Why Unstructured Classification Matters?

Clay Shirky once write a great article about the importance of user defined classification. This is even more important for the socially networked "Web 3.0" CMS. Of course a CMS will let the publisher classify content by format/function (ie; content type) and topically (ie; categories,sub category,etc..) -- But the new CMS will also let me "tag" my content and generate another map it.