I've had very limited experience with Zope (and Plone) - a client of mine uses Zope as a basis for an enterprise web app and loves it, he did find it had a lot to get your head around at first, but said it's one of those things that you just look at and think, 'yes, this is how it should be done'.

I setup a basic Plone site when I was considering using it for a client, it is very powerful and elegant, but (as an intermediate-level PHP coder) I also found the sheer complexity of it intimidating.

I get the impression that Zope is coded by professionals who think about things like scalability and security, whereas solutions like PHPNuke are written by hackers who are interested in cool features and buzzwords rather than whether it's done right.