Google PuSH: What Is PubSubHubbub?
An overview of PubSubHubbub, a simple, open, web-hook-based publishing/subscribing protocol & open source reference implementation. Brett Slatkin and Brad Fitzpatrick demonstrate what PubSubHubbub is and how it works. Found at YouTube from GoogleDevelopers via 20e10.
“PubSubHubbub” may be hard to read but understanding this protocol quite simple. Try to find time knowing how this works and you'll be amazed.