I'm re-posting this here to force me to deal with it more productively. Jon Udell totally nailed what's wrong with deeply structured taxonomies, and the different bags-of-keywords approach successfully employed by Flickr and del.icio.us.
What needs to be done is to show how the bags-of-keywords approach could be employed in such a way as to allow the librarians of the world to relax (i.e., can it provide an efficient way of navigating a large-scale repository or repositories, or is it effectively limited to small scale - personal or workgroup level repositories? Gut says it could scale, but there isn't enough data to get the library geeks to chill.)
InfoWorld: Collaborative knowledge gardening: August 20, 2004: By Jon Udell