I ran across an interesting book on Amazon recently – Tagging: People-powered Metadata for the Social Web by Gene Smith. Written in the dark ages of social media, 2008, this book still offers a relevant and insightful look into the power of people for tagging the internet universe.
Touting tags as a springboard to new ideas, Smith explores tagging for classification, visualization and exploration. As one might expect, taxonomies and folksonomies are discussed as well as real world examples from Flickr and Amazon.
As more and more metadata is generated collectively, it is worth revisiting this resource.