Tuttle SVCTom Hoffman has an interesting piece about Dave Winer's "Share Your OPML!" campaign.
In comparison, "Share Your OPML!" is simplistic, even by the standards of Dave's earlier work, requiring users to manually export an OPML list from their aggregator and submit it to a central server. Only the subset of geeks who are game to try every blog gadget that come down the pike (which includes me) will ever do this, and that subset is the best understood and most easily studied part of the blogosphere.