Atom 1.0 plugin replaces all WordPress feeds. RSS will no longer be available, and Atom 1.0 will be served at most of the generated URLs that previously served RSS. This includes blog?feed=rss and blog/feed/ links. Navigating to blog/wp-rss2.php will still give the RSS feed. Users should edit their theme so that the blog/feed link is labeled as Atom (or Feed), and there is no link to blog/feed/atom/. The plugin is based on James Snell's Atom 1.0 templates.
More info: Home Page