Wired investigates how RSS is developing as an advertising medium in 'RSS Feeds Hunger for More Ads'.

'Purists' freak at the notion of incorporating ads into RSS.  David Winer doesn't go quite this far in the Wired article, but cautions:

"...let's be kind to RSS; don't try to exploit it," he said, adding that readers who were turned off by an ad-laden RSS feed could simply opt out.

This last point IS the point.  RSS ads are neither 'good' nor 'bad'.  Those who monetize content have a choice: add ads to RSS and risk losing feed subscribers.  Conversly,  if a subscriber does not perceive there is fair 'value exchanged', i.e. content for ads, they can opt out.  Easy.

There is nothing new here from the perspective of the publishers/content/media owners.  They have always had to find the optimum balance between content and advertising whether it be TV, radio, print, web, etc.  RSS is no different. 

An example of how some publishers are risking the loss of RSS subscribers is provided by Tim Bray who points out what he describes as 'cheating' by Infoworld....

"The current Infoworld feed is cheating, though. The stories keep changing and coming up again in the aggregator, when all that’s changed is the ad....

So let’s hope that this is just a bug, because if they’re going to switch the ads on their stories, someone’s going to have to set things up so the aggregator knows this isn’t a real change. Otherwise I unsubscribe."

And that's the deal.  For Infoworld and the rest of the publishers the choice is simple:  take the p###, lose subscribers.