Delicious Reading Lists
Reading Lists are an idea so dead simple one wonders why it hasn't been there ever since: instead of just downloading someone's OMPL list of feed subscriptions and feeding it into an aggregator once, like it normally get's done, you subscribe to the subscriptions list. Most aggregators don't support this yet, though.
Danny Ayers has a simple XSL file to transform del.icio.us feeds into basic OPML and uses the W3C XSLT Service to process them - voila, dynamic OPML that gets updated each time an item with the right set of tags (e.g. "readinglist" + "readinglistname") is added to one's del.icio.us account.
Of course you can use such OPML files for more than just feeding aggregators: OPod and Taskable render OPML files in Apple Finder or Windows Start Menu styles, Sjoerd Visscher and yabfog.com have PHP scripts for OPML rendering.
