OPML Reading lists
Reading lists are OPML documents that point to RSS feeds, like most of the OPML documents you find, but instead of subscribing to each feed in the document, the reader or aggregator subscribes to the OPML document itself. When the author of the OPML document adds a feed, the aggregator automatically checks that feed in its next scan, and (key point) when a feed is removed, the aggregator no longer checks that feed. THe editor of the OPML file can update all the subscribers by updating the OPML file. Think of it as sort of a mutual fund for subscriptions. by Dave winer
It’s a kind of having somebody else taking care of your aggregator subscriptions adding new feeds and removing obsolete ones for you. i.metaRSS allready supports the OPML import and export but it’s only limited for local files, but having the possibility to import web based OPML was in the plan and now we should add not just a simple import but a regular check like a feed subscription. And I would add that a filtering ala iResearch based on certain OPML Reading lists could be a great feature.