[alexandros]

The article mentions that the explicit unsubscription of PuSH is an advantage over the implicit approach of rssCloud. With garbage collection being a major problem of publish/subscribe in distributed systems, the author needs to mention how PuSH deals with it in order to assert superiority. Without acknowledging it, the credibility of the article is limited

[curio]

That's an important point. You can see how PuSH handles it here: http://pubsubhubbub.googlecode.com/svn/trunk/pubsubhubbub-co...