Google announced that Google Reader begun adoption of the PubSubHubbub protocol, beginning with the publishing of shared items. All shared item pages have feeds, and now all of those feeds’ll ping a hub (and there's a <link rel="hub" .../> element in them). Means if web app developer would like to more efficiently and quickly monitor Reader shares, you just’ve 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. One place that takes advantage of this pinging is FriendFeed, which shows shared items within a few seconds of pressing the "Share" link in Reader.