PubSubHubbub is a nice solution to the increasing problem of aggregators struggling to ever get around to parsing your WordPress RSS or Atom feed during its continuous polling thanks to the ever multiplying number of blogs they might need to serve. Basically put, it is a simple, open, server-to-server web-hook-based publish/subscribe protocol that can be seen as an extension to Atom and RSS.
Parties speaking the PubSubHubbub protocol essentially get near-instant notifications via webhook callbacks on feed URL updates and this thus frees up the listening parties from having to continuously poll the publishing party.
Anyhow, WordPress has released a great little plugin courtesy of Joseph Scott and Automattic called PuSHPress that basically adds PubSubHubbub capabilities to your WordPress-powered site, turning it into a PuSH server and making it capable of thus entering directly into PuSH partnerships with other listening PuSH parties.
It’s easy to install, simply add a new plugin via your administrator dashboard, search for PuSHPress, install and activate. Couldn’t be any easier (and don’t worry, it won’t change any outwards/visible functionality on your site).
Related Link: http://wordpress.org/extend/plugins/pushpress/