Google added the initial PubSubHubbub protocol, support in FeedBurner. 'Hubbub is an open specification in draft for web-scale publish and subscribe. The protocol can be used to transform any existing Atom and RSS feed on the web into a real-time stream. Feeds with PingShot are automatically enhanced with the PubSubHubbub protocol. If you’re not using PingShot service, visit feedburner.google.com, from Publicize tab for your feed, select PingShot, and click the [Activate] button. From AdSense, go to Manage Ads, then click View Feed Stats link, and click acitvate. We'll add the required discovery elements to these feeds and notify a Google-run Hub, running on App Engine, of publish events. We also convert any pings we receive into 'Hubbub events.

More info: PubSubHubbub protocol