In looking for some use cases information for Drupal, I came across the following blog post about Plone versus Drupal: http://m.odul.us/2007/09/02/plone-vs-drupal-take-one It's worth reading not just to see how one person compares Drupal to Plone, but to see where Drupal is lacking some interesting capabilities (e.g. being able to generate Plone modules using UML).