Andrew Grumet has built Similar Feeds, a neat demonstration of collaborative intelligence that uses the Share your OPML development interface to reveal which feeds are also popular among readers of a given feed. The handy 'tweak results' feature lets you filter out the most popular feeds in case you're looking for something you might never have seen but that relates to a given feed. Compare the first link above with the results at level 2000. _(via Lilia Efimova: http://blog.mathemagenic.com/2004/02/14.html#a1084)