In their release note, the Joomla! developers remark that
The next phase offers the opportunity to bring together the code created, lessons learned, and momentum gained, to build something truly great. It took us tens of thousands of hours, thousands of revisions, and hundreds of people to get to this point. It has been a remarkable journey filled with fun, discovery, and enlightenment where everyone has something to offer and anyone can contribute.
I don't think we could have said it better ourselves! And, with the release of Drupal 6 right around the corner, I'm sure we all know exactly how proud they are of a job well done.
As our Joomla! friends have said before, we're friends with common goals, and we are all on the same side. We both value PHP, MySQL, GPL licenses, community based collaboration, open standards, accessibility, low-resource requirements, ease of use, and an extensible and modular design. And, ultimately, we all agree that open source matters.
From the Drupal community to Joomla!, Congratulations!