Basically the PubSubHubbub protocol turns web feeds in to real time streams and as developers adopt the protocol, feeds will appers in readers in near real time.
Google Reader, my favorite reader has also implemented PubSubHubbub. You can find a link to at the bottom of this article.
The protocol in a nutshell is as follows:
- An feed URL (a "topic") declares its Hub server(s) in its Atom or RSS XML file, link rel="hub" ... . The hub(s) can be run by the publisher of the feed, or can be a community hub that anybody can use. (Atom and RssFeeds are supported)
- A subscriber (a server that's interested in a topic), initially fetches the Atom URL as normal. If the Atom file declares its hubs, the subscriber can then avoid lame, repeated polling of the URL and can instead register with the feed's hub(s) and subscribe to updates.
- The subscriber subscribes to the Topic URL from the Topic URL's declared Hub(s).
- When the Publisher next updates the Topic URL,, via. the publisher software pings the Hub(s) saying that there's an update.
- The hub efficiently fetches the published feed and multicasts the new/changed content out to all registered subscribers.
Official Google Reader Blog: PubSubHubbub support for Reader shared items