We have a Library, but no Librarian. Users may browse, but they can't ask for help. There isn't even a card index. People want their listing to appear in multiple categories. This is equivalent to wanting to associate multiple keywords with the entries - which would be a useful extension.
People classify their entries poorly.
This depends to some extent on how clear and intuitive the classification system is, although some people apparently refuse to spend any time trying to understand it. The greatest number of mis-classifications are from commercial entities seeking to publicise their products and services. In addition, other means of populating a catalog, by spider and by surfing, reading newsgroups, mailing lists, etc, may also be used. This could be partially automated by program to extract URLs from these sources, compare them with the catalog URLs, and those not found can be added to a list for later investigation by a human. The enumerative scheme is based on the concept of a universe of knowledge which is divided into successively narrower and more specific subjects.