Interesting discussion about making OPML dynamic like the RSS feeds that an OPML file aggregates.  This would allow the distribution model of OPML to be changed to a subscription model.  In TagIt, we've sort of got this without having to change the way feed readers work.  Since a bibliography is capable of creating an RSS feed, they already can be read by the feed readers dynamically -- that is, the readers can get new content as the bibliography is updated.  And since the bibliography topics themselves are simply posts, they can be consumed via RSS.  The only things I'd need to do in the code is

• update the timestamp on the bibliography topic whenever a component is added or edited
• give access to an rss feed of just the bibliography topics (by user or by TagIt instance)