Boxes and Arrows: Creating a Controlled Vocabulary is a useful primer for anybody considering building a taxonomy or controlled vocabulary from scratch to support Web content classification and navigation
This is one of those tasks that sounds simple and is often slipped in to development projects almost as a freebie, but anybody who has tried to do it (especially with a group of stakeholders) will concur that it is harder than it looks
Thanks to Boxes and Arrows for a comprehensive article with good links.