Google’s John Mueller confirmed on Twitter that Google still supports PubSubHubbub, now known as WebSub. WebSub basically pushes content and changes, it is a real-time notifications of changes protocol. Wikipedia defines it as an open protocol for distributed publish/subscribe communication on the Internet.
It was pretty popular in the early days of blogging, to get Google blog search to find your content faster, as well as other blog search sites. Now Google is pretty quick without it, but John said Google still supports it.