Kuro5hin member switches to Zope
Kuro5hin: Switching from PHP to Zope/Python
A pretty good set of reasons for switching. I don't think someone needs to completely abandon PHP though. There are scenarios where using PHP is better than Zope, simply because Zope is generally slower than PHP.
Use the right tool for the job. Zope is the right tool for the content management job. PHP is good at pushing dynamic pages out fast. And Zope is a good way to make fast PHP pages, because after all, PHP pages are content, and your Zope CMS is a good way to manage those. :-)