The official Google Webmaster Central blog has a post on it titled Taking feeds out of our web search results.
With this post Google defines a precise policy regarding the indexing or no-indexing of feeds. In summary, Google is officially not going to index any feeds, with the exception of multimedia feeds such as Podcast feeds.
The most interesting part of this to me was the rationale – it turns out that the majority of non-multimedia feeds represent content already on HTML web pages, and many times these pages contain additional content beyond what is in the feed itself. When Google sees a scenario like this, the web page with the content, and the feed with the content are pretty much duplicate content for each other. Given that the HTML page has a strong chance of being the superior solution.
This happens less frequently with multimedia feeds such as Podcasts. For that reason, Google will continue to index Podcast feeds. Publishers who want their Podcast feed Noindexed can do so can follow the Yahoo Guidelines, or if they use Feedburner they can easily set this up within Feedburner.
I think it’s great that Google has defined a clear policy for this. Now webmasters know exactly what they are dealing with. Of course, there will be some webmasters who want their (non-multimedia) feed indexed, and that have relied on that traditionally. However, this is no longer an option, and it behooves such webmasters to figure out how to get that content rendered on an HTML web page which is crawlable by Google.