Google Reader now publishes feeds in real time. This means posts appear in Google Reader as soon as they go live on a site. These real-time updates will however only work for PubSubHubbub-enabled blogs.
A new update to Google Reader allows you to follow changes to any website.
Google Reader will create its own custom feed for sites without a RSS feed.
Google launched a new feature yesterday which enables the search engine to scan RSS and Atom feeds for the discovery of new webpages.
RSS/Atom feeds is a mechanism for content publication and allow readers to easely check for new content from publishers. By scanning these feeds Google will get new pages into their index more quickly than traditional crawling methods.
Adding feeds to current crawling techniques might lead to content being indexed faster.
(source: Google Webmaster Central Blog)