flavor of the hour could be used as a channel for worms/viruses/hacking.
Here's a good example.
Yes, RSS could be a vector for malware but it's not a likely one. It's not like we constantly wander the Internet in search of new feeds. For the majority of people, their feed sources remain constant. Barring a web server compromise at one of those sites or the author does something really boneheaded, there isn't much risk of worms or spyware sneaking in via the RSS feed.
Of course, if the author embeds crap like advertising in his/her feed, then it's another story.