One of the reasons I like RSS feeds is that they are largely free of ads. pop-ups and other such pollution found on the browser side of the internet today.
I knew that was too good to last -- Google is experimenting with AdSense ads in RSS feeds. So, that's one horseman of the internet apocalypse to ride into RSS town. The others aren't far behind, I'm sure.
There's some debate as to how effective advertising in RSS feeds will be, seeing that ad blockers are already being developed for RSS readers.