Google has moved RSS adverts into a wider beta, and Robert Scoble has been considering the benefits or otherwise of them. And he ranks types of feeds from worst (Headline only, with ads) to best (Full text with no ads).
Deciding whether or not to put adverts in your RSS (and indeed if your feed has all your text or just the partial text) is, I think, a matter of what you’re trying to do with your content. To bring it to total black and white, are you trying to make money, or get your ideas out?
Reality, of course, is shades of grey. For one thing, if you go the total black option (headlines only, ads in the feed, and presumably more ads on the site — since that’s the only reason you’d want to provide only headlines in the feed) then unless your content is pretty damn compelling, you’ll get no readers (at least not from feeds, and this is increasingly the way people consume their web sites), and thus no money, and your content goes nowhere.
Other end of the scale (full text in feeds, no ads anywhere) is okay, as long as you don’t get snowed under by readers, and end up paying so much in bandwidth that you can’t afford it anymore. Not likely these days, but theoretically possible, especially if your content is multimedia.
For most of us, I suspect, the balance is somewhere closer to white than black.