People always ask me why would anyone pay for Agility when they can get Joomla or Drupal for free.

Here are the main points:

• Open source software is not owned by anyone, so no one takes ownership over it
  • No tech support
  • No neck to ring if something goes wrong
  • Spotty documentation
• You really have to be an expert to sift through all of the modules and add-ins to get the ones you want
• They are both very confusing and difficult to use for end users
• It is hard to find a developer who is experienced enough to implement it right, and if you do, they disappear after the project
• It is very difficult to keep the Drupal and PHP versions up to date which makes it harder to expand your site and and drastically reduces site performance over time
• You still have to host the website and the software somewhere which costs money

Also, Dan Knauss explains how Joomla is missing the boat in CMS.  He argues that Joomla doesn't even classify as a CMS:

http://www.alltogetherasawhole.org/profiles/blogs/the-competition-joomla-is

And then there are posts on RoboZen and Bivings Group about why Drupal sucks:

http://robozen.com/technology/drupal-sucks/

http://www.bivingsreport.com/2009/so-why-does-drupal-suck/

And of course the famous post on the Drupal.org site about the problems with Drupal:

http://drupal.org/node/34421