I was looking at the Joomla site today where I came across this article by the Joomla team about their license (the GPL). I appreciate the fact they are taking a good stand for Free Software. They’ll probably end up and take a hit from parts of the community though.
I think what they are saying is that all modules, extentions, etc… to Joomla also need to be licensed under the GPL. I don’t know if that is right or not, but it is their understanding of the GPL.