Now Google Reader has adopted PubSubHubbub protocol.
Beginning with the publishing of their shared items. All shared item pages have feeds, and now all of those feeds will ping a hub (and there’s a <link rel=”hub” …/> element in them). This means that if you (as a web app developer) would like to more efficiently and quickly monitor Reader shares, you just have to subscribe at the hub to be notified of changes in real-time. If you want to learn more about PubSubHubbub and how it works, see the site and protocol definition.
Adding PubSubHubbub to your application is definitely a low-effort but high-payoff way of making the Web faster and more efficient.
Read More: Google Blog