I had the pleasure of visiting the Detroit Joomla! Group last week after being extended an invite by Shane Sevo to start a discussion between our two groups of how Drupal and Joomla compare and contrast.
Too many times the Drupal vs. Joomla debate is more religious than anything. We have all chosen our specializations and have our biases, but those don't necessarily prove useful to our clients. Instead, it's important to understand there are times when one tool is a better fit than another and the only way to do that is to understand the tools at your disposal.
I'm looking forward to visiting the Joomla!Detroit group at their next meeting in September and will be giving a basic demonstration of what Drupal is, how it works, and where it fails and succeeds. I'll also be going over some common contributed modules that almost every Drupal site uses including CCK, Views, and more.