Plone/Zope are difficult, but the compactness of Python combined with the clarity of the design make digging in not terribly difficult. Understanding every aspect of the stack is difficult, Zope is everything from the HTTP server to the (object) Database, to the templating language (TAL). All those different pieces are difficult to keep in your head, but I'd still give it a hand up over most Java stacks: keeping pieces of the system in your head is easy.