FWIW, categories can also be very useful for generating offline wiki snapshots. For example, for education I might want to ensure that my wikislice has all the articles related to chemical elements. One reasonable way to do this is to grab all the articles in [[Category:Chemical_elements]]. In order to efficiently make wikislices for the many different languages OLPC targets, it uses inter-language links to automatically 'translate' the root set for the wikislice. So language links for categories help. --scott
ps. OLPC's wikislice-puller doesn't actually use categories at the present time; instead it starts from [[Chemical_element]] and hopes that all the chemical elements are linked from (the translated version of) that page. Using categories would likely be an improvement.