The m.odul.us review has garnered a handful of comments, but it probably deserves more. For those who are looking at any CMS, not just Plone and Drupal, a read-through will give you a good idea of what a sensible evaluation must touch upon. Just to give you an idea of the breadth of Matt's piece, here are his headings:
- Easy Publication to the Web
- Flexible Information Architecture
- PHP vs Python
- LAMP vs Zope
- Scale, Speed, and Deploying
- Hosting Requirements
- Contributed Add-ons
- Documentation and Community Support
Drupal is a community content management system, and it largely farms out other tasks (e.g., asset management, CRM, etc.) to other web apps, choosing instead to integrate with them. This is a reasonable stance; Drupal is a CMS, and it integrates into a larger world of Apache served web applications.
Plone, however, looks at a most web application problems as specific instances of content management. Thus, with Plone, is it not absurd to develop extensions to handle your asset management system or your email newsletters (complete with server). Plone is built on a powerful application server and it makes sense to leverage it and your data once you're used to programming for Plone.