I've put together some quick UML sequence diagrams that cover the main scenarios. http://www.xpdeveloper.net/pubsubhubbub
Click on the diagrams for the websequence.com source (Remix and Share, give me mention + contribute improvements back). PubSubHubBub Overview Sequence Diagram by Oliver Bye is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. Oli Bye
