I've been using Dave Slusher's perl iPodder and noticed lots of duplicates in my iTunes playlist. There's Applescript code in the Mac iPodder that removes them on each run. I tried putting my script into Dave's, but still don't grok how the syntax for the applescript calls work in perl.
Dave has also been making beautiful use of RSSfeatures.
Pieter Overbeeke has released an iPodder that you can run on windows with iTunes. It automagically downloads all mp3 enclosures from rss feeds and puts them into your iTunes library.
I have no way of testing Pieter's script, but if it works as advertised, we just opened the iPod Platform to a huge audience.
Next step: getting from iTunes to non-iPod mp3 players.