[I]f you are providing me with the full text of the article in my aggregator, then I'm willing to trade you my eyeballs for an ad. However, if you're just sending me the headline with a one- or two-sentence description, then that's the ad. Your intent is to get me to go to your site to read the full article, at which point I will see the ad (probably lots of ads), and the transaction is complete - I clicked onto your page and became a number you can sell to your advertisers and in exchange you let me view the content.
I agree with Jenny in this distinction. Syndication implies you're giving me the thing, not just a link to it. What actually happening with most RSS feeds is we're pulling down a "teaser" and we'll go read the article on site if its interesting. In that case, the ads can exist on the site and when I read the article, I'll see them. Frankly I mostly only want to see summaries in RSS anyway.
Even so, if InfoWorld or the NY Times, or someone else wants to put ads in my RSS feed, I'll survive. If they're too obnoxious, I'll unsubscribe. I'm just not going to be able to get too worked up about this.