I've come across a couple of good articles for you metadata-heads out there:
How to Make a Faceted Classification and Put It On the Web by William Denton. This is a great step-by-step guide to faceted classification, and it includes details on using both XML and relational databases to store the facets. Well worth a read if you're embarking on a project that might use faceted classification.
The Information Management Weblog, maintained by Karl Nelson, covers a variety of information related topics, including content management, knowledge management, web development, and anything else that looks interesting.