The Official Webmaster Blog explores the difficulty that webmasters face due to adulteration of the search results by RSS/Atom feeds that affect user experience by "crowding out their associated HTML pages in Google's search results."
The say that the feeds hamper user experience on two counts;
- Feeds increase the likelihood that users see duplicate search results.
- Users clicking on a feed may miss valuable content available only in the HTML page.
That's why they "…prevent feeds from being returned in Google's search results, with the exception of podcasts (feeds with multimedia enclosures)."
The reason for allowing podcast to continue is "…because we noticed a significant number of them are standalone documents (i.e. no HTML page has the same content) or they have more complete item descriptions than the associated HTML page." But for those webmasters who'd like their podcasts to be excluded as well, have the option to do so by using "… Yahoo's spec for noindex feeds. If you use FeedBurner, making your podcast noindex is as simple as checking a box ("Noindex" under the "Publicize" tab)."
One drawback of this approach that they admit to is "…there are a few non-podcast feeds out there with no associated HTML pages, and thus removing these feeds for now from the search results might be less than ideal."