Blogs that run on WordPress.com now automatically have the RSSCloud feature integrated into them. WordPress.org users can download a plugin from here: http://wordpress.org/extend/plugins/rsscloud/.
RSSCloud is a service that adds a cloud feature to RSS feeds. As soon as an author writes a blog post or news story, an update ping is sent to a cloud server. The cloud will determine whether that post is being subscribed to. If someone is subscribing to them, then the RSS aggregator is updated. This all happens within a second. The RSSCloud protocol was made by Dave Winer, the inventor of the original RSS specification.
Matt Mullenweg, founding developer of WordPress wrote about the changes on the company blog. “There?s only one reader so far (River2) that supports RSS cloud, but we expect there to be more in the future. We?re also going to be supporting other ways for people to get push notifications (Jabber, email, Weblogs.com pings, SUP, pubsubhubbub, Twitter? who knows what else) so people will be able to find out about and visit your new blog posts as soon as possible, making blogging a more real-time experience. Since RSS Cloud is so easy to add to RSS, it seemed like a good place to start,” wrote Mullenweg