I don't think I ever explicitly mentioned it here on FFG, but category-based feeds work here, too, and, indeed, work on any dynamically-served Blosxom blog. It's one of those cool things I always took for granted, like oxygen. Anyway, if, for example, you like my music posts but think I'm completely full of it whenever I talk about technology, you could subscribe to my music subfeed at http://www.freeke.org/ffg/entertainment/music/index.rss20. Just look for the "breadcrumbs" after any given post to let you know where in my hierarchy a given sort of post resides. The cool thing is that those feeds can start anywhere in the hierarchy, so http://www.freeke.org/ffg/entertainment/index.rss20 would get you all of the posts about not just music, but any other "entertainment" subcategories, like books and food.
Of course, this being Blosxom, these subcategories work not only for RSS 2.0, but for any content type I've built a flavour for, for example RSS 1.0, or HTML, or Atom, or printer-friendly, or mobile-ready. Even "cool URI's" like http://www.freeke.org/ffg/entertainment/music/dbsweden work (they give you the HTML rendering.) Not bad for a few hundred lines of Perl, eh?
Just remember, next time someone tries to sell you a "revolution", check for prior art. :)
If anything can go wrong, it will.