There is a new version of Plone out for some weeks now as well as a roadmap for future releases. The homepage of plone.org has also been redesigner to emphasize the key selling arguments of the Plone CMS.
I have seen in the “inner workings” of a number of content management systems. I think Plone is one of the highlights in terms of the beauty of its technical design. There is alot one can learn from Plone conceptually.