Idealware published a nice overview piece "Comparing Open Source CMSes: Joomla, Drupal and Plone." 

 Open source content management systems can make creating and managing your website a lot easier - and there's no licensing fee involved.  But which should you use?  We look carefully at Joomla, Drupal, and Plone to compare their strengths and weaknesses.

Read the article at Idealware:   http://www.idealware.org/articles/joomla_drupal_plone.php