Yahoo news has an interesting article on worm propigation via rss feeds.
"David Sancho, senior anti-virus research engineer at Trend Micro, warned that RSS feed hijacking will become commonplace when Microsoft Corp. ships Internet Explorer 7, a browser refresh that will feature built-in RSS support.
In a white paper titled "The Future of Bot Worms," Sancho said the IE7 release "will open some interesting possibilities to worm creators." - Yahoo!
A whitepaper by Trend-Micro describes the concept more in detail.