It is the news that the Joomla community has been waiting for since hints of a changed licensing stance first surfaced back in April:
http://www.joomla.org/content/view/3510/1/
“We have decided to stay with the licence that made Joomla! possible. Unanimously supported by the core team and supported by the Open Source Matters board, this confirms that both Joomla! 1.0 and Joomla! 1.5 are released under the (pure) GPL.
We’ve also decided that we do not have the authority to publish Joomla! under a version of the GPL that gives exceptions for proprietary extensions. “
It is a brave move and one with very few precedents in the Open Source world. It will thus be a fascinating few months for Joomla, watched closely for lessons by people running hundreds of other FOSS projects.