Taxonomy extensions - CCK Freetagger looks interesting for free tagging of content types.

Quoted: The Taxonomy module organizes taxonomies into vocabularies which consist of one or more terms. Vocabularies group terms that describe an aspect of the node.

Interesting post on tagging systems; why they work well on LibraryThing, and poorly at Amazon.

Takeaways:
- People will tag, when it benefits themselves, but not if it only benefits others.
- You need a critical mass of tags to be useful to community and overwhelm spam-taggers and opinion-taggers.
- You generally want over 100 tags applied to a book to get both highly relevant and complete tags represented.

Currently 43 comments on this post. Our friends at Peerworks (Shel Kaphan's non-profit tagging project, was one of the first to respond.

If Digg used a tagging system, rather than a fixed set of categories, users wouldn't have to go begging for a new featured area - it could just be organically grown (as it is on Blue Dot).

Quoted: Digg users have begun calling with increased volume for the creation of a special section of the site designated for photographs and pictures. Two ...

Quoted: Clay Shirky's writings about the Internet, including Economics and Culture, Media and Community, Open Source

Explanation of the (rather complex) Wikipedia category system.

Downloaded to my MP3 player - this was a VERY GOOD talk. I really have a feel for Jimmy Wales (founder of Wikipedia) personality and a better idea for the true success principles behind Wikipedia (it's much less chaotic than it appears).

click to play

Great lecture on tagging. Really gets going about 20 minutes in. Shirky

Quoted: each item could be assigned to multiple categories (which could themselves organized into hierarchies), either by the user or automatically through classification rules