Despite Zeldman's demurs, I'm also working on a "tagging" system (sometimes called "folksonomies") for Poetry X so people can tag poems with relevant keywords.
You see, Jeffrey, it's not that we have to abandon traditional parent > child relationships in our navigation design - it's just that we can supplement our structure with something more flexible and democratic.
I'm not about to abandon editorial classification, I'd just like to give users the option of deciding within the community what is and isn't relevant.
Also, as far as tag "clouds" go I don't know how useful they are, as the positive feedback loop aspect (things rated highly because of clicks tend to continue to remain at the top of the list due to people clicking them on the list - like our Top 50 Most-Read Poems feature at PX) but I see user added tags as a great way to search for things, and for content sites to post the most relevant tags for each item/monad it exciting. People looking for "love poem" can click on it and see other things that other people classified as "love poem."
Maybe JZ and I are talking about two different uses for the same thing, but I think he's just giving in to the "not invented here" acrimony.