WordPress has ventured into real time before with support for RSSCloud, but thanks to PubSubHubbub, all posts from any WordPress.com blog will appear in services like Google Reader, Bloglines, Friendfeed and Netvibes in real time.
You don’t have to be on wordpress.com to make this happen. WordPress are also announces an official plugin to enable PuSH support for any wordpress.org blog. You can download that here.
PubSubHubbub is an open protocol for distributed Publish/subscribe communication on the internet. The main purpose is to provide near-instant notifications of change updates, which would improve on the typical situation where a client periodically polls the feed server at some arbitrary interval.