For my test run, I generated OPML files for a LiveJournal users's list of friends. Most of my friends have blogs hosted on LiveJournal. I wouldn't read them at all until I found out you can stream their through RSS. So then I'd read Melanie's. Now I have them all imported to NetNewsWire using this greasemonkey script. Right now, it does not distinguish between people, communities, and feeds but I don't mind unsubscribing items as much as I mind manually subscribing to one feed at a time.
Now that I know it works, I can think of much cooler applications of this combination.
Update: Greasemonkey script has been updated to support LiveJournal's new URL scheme. Yeah I'm a few months behind on this one. Thanks to Scott for pointing it out to me.