PubSubHubbub (also known as PuSH) provides a way for services to subscribe to new entries in feeds (RSS & Atom) when they are published. This allows for new content to be distributed in a rapid fashion and reduces the need to regularly poll feeds to check for new content.
When you publish a new post, WordPress.com gathers up the lists of PuSH subscribers for the feed and sends out the new content to them directly. Because the content of the new post is sent directly to the subscriber they aren’t required to fetch a copy of the feed to get the new data.
How do I enable this for my WordPress.com blog?
It already is! Every site hosted on WordPress.com includes support for PubSubHubbub.
How long does it take from the time I hit the publish button until the notifications get sent out?
Our observations have been that they go out within a second or two.
Where can I learn more about PubSubHubbub?
Check out http://code.google.com/p/pubsubhubbub/ and the PubSubHubbub specification.
You can also see rssCloud.
