Readers can leave messages for the authors attached to the diary entries. A nice implementation. I think this is more toy than Info Architecture tool at this point, but it's definitely a way to traverse a spawling web site. Automation cannot currently index the Internet. Human editors are needed, but costly.
Indvidual sites have an incentive to index, but no incentive to use a common scheme.
An index may be a public good. To combat 'spamdexing,' overloaded keywords, hiding keywords and other tricks used to fool the search engines. Dvorak suggests we should go the route the librarians forged years ago and settle on a limited search vocabulary. My friend David Bratman, a librarian who specializes in cataloging, agrees that a set vocabulary is a good idea. The arms race between the indexers and the morons who think you're interested in whatever crap they are selling continues.