There is a lot of talk about tags, here are some links, once it is geekess only:
More on Technorati tags by Suw
Cheap Eats at the Semantic Web Café by Burningbird
On Tags and Ontologies by Stéphanie
Categories and Meaning by Adina Levin
Well, what do I think about tags? I think they are great, as it is really a bottom-up approach which works, see del.icio.us and technorati.
Somehow we are lacking „role“, but I do not know how to do it yet, without making it too complex again.