I am taking part in the development of a PHP CMS (yeah I know you are like, meeh). It is currently using simple tags for tagging content. What I want to do is push the whole thing to using Taxonomy but I am not sure on what to pay attention to, or how to go about structuring the whole vocabularies/terms. I'd love to be able to keep the user interaction close to that of the current simple tags and at the same time allow for more advanced usage by power users. The Drupal and the Wordpress taxonomy systems are being reviewed at the moment and they provide valuable resources. Nevertheless, it could be that someone has some simpler and more appropriate thoughts on this matter.