Like the title, a unique article by some of the best on social tagging systems (picked up from Seb). Despite taggings increasing popularity, this is little researched area. The authors offer a taxonomy of tagging systems to help analysis and design of such systems. The system identifies seven dimensions including tagging rights, support, source material, aggregation, object type, resource and social connectivity. By the use of this taxonomy, the researchers concluded that tagging systems such as Del.ic.ious and Flickr are in fact very distinct. Given the increasing deployment of such systems, hopefully more work can be done on the development of these taxonomies to give a better understanding of its affordances and constraints.