The Google Webmaster Central Blog announced that Google will no longer include RSS feeds in their search results, with the exception of podcast feeds.
The reasoning behind Google dropping RSS feeds from the results is that it is very likely that the RSS feed is a text duplication of an html document, and when users view RSS feeds, they may not be able to render the XML format in their browsers.
A quick way to tell if RSS feeds are out of the index is to do a site command on a popular RSS feed producer, FeedBurner. Google shows zero results for the site:feeds.feedburner.com command, while Yahoo shows me 8,461,464 results.
I know Google has been working on removing raw RSS content from the main web results at least since mid-September.