John Robb on his Weblog Network blog was looking for a top level hierarchy. I wrote him:

As for structure, this is a very difficult thing to do. I suggest you borrow someone else to start and modify as you go along. I sat in on hours of debate for the metadata controlled vocabulary for educational "lesson plans" and other materials (http://www.geminfo.org/Workbench/gem2.html). So look at Yahoo, Google, Feedster, About and make a choice.