I can totally understand the thoughts behind this move. But for me this comes far too late. There has been kind of an agreement between the Joomla Core Team (and before the Mambo core team) and the commercial developers. Commercial extension are a vital part of Joomla community and were fully accepted by the dev team. People have been relying on this for YEARS now and have built there livelihood around this. To change the view on this point by 180 degrees from the dev team takes sooo much away from the commercial developers and puts them in the "you are a bad one" corner. This is just not fair. I am not a developer in any kind, just a Joomla fan and I have loved the fact that there were commercial components out there with a high level of quality for a small price. This way I, as an end user, am not forced to pay someone for custom development.
Another question comes to my mind. When I hire someone for custom development of a component I will be forced to release this component under the GPL. This way I have to pay for it and others can use it for free. This will certainly stop many people from hiring developers at all. Or do I see this wrong?
Why do there have to be such "earthquakes" in the Joomla community from time to time? This throws Joomla back every time. This way people will never trust OS software because You just cannot rely on the people behind it when there such moves from time to time...
It will be very interesting to see where this takes Joomla. What will happen with joomla.org when the dev team announces to make their site compliant? I guess the whole extension directory will disappear because it is based an "bad extensions". What about the huge amount of work that people have put into that? How will they feel? This is a punch in the face of so many.
Sometimes You just have to stick with a way You took in the beginning. It is honourable that the core team wants to correct mistake they made but sometimes it is just too late for that. Take it like it is and stick with your initial way!!

What is sad about this news is that, IMHO, the core team that developed Joomla felt that the development community that built the great extensions that made Joomla popular were not a necessary group with whom to discuss the issues with prior to this "bold move." There has been precious little explained as to the circumstances behind the team's sudden shift from a non-GPL business model and practice to an all GPL requirement that caught both the developers and the user communities completely by surprise. The repercussions are being felt now -- many of the most popular extensions that made Joomla the greatest choice for rapid web site development have been removed from the extensions directory and gone for good. This decision was not only premature but arbitrary and is acting to threaten the very existence of the project.

What is even more unfortunate is that the statement whereby the core team believes it has no choice but to require all extensions to be GPL compliant does not provide full disclosure of the truth, IMHO. Apparently the Joomla team seems to have obtained its legal advice from the Free Software Foundation and have come to the conclusion that extensions (add-ons/plug-ins) to Joomla are "derivative works" under law and subject to the GPL license. This appears to be debatable at best, with the FSF obviously taking a most extreme position. At present, there is rarely a post in the Joomla forums where the team and moderators do not remind users regarding their understanding of the use of Joomla that they are not lawyers and that the users should seek legal advice to understand more.

So what is the moral of this story? Not caring to communicate with your community and developers can prove to be fatal to your efforts. The sadder part? There still is no communication to find a reasonable compromise and it appears that the core team does not believe that the incredibly talented group of extensions developers were significantly responsible for Joomla's growth.

The link to the Joomla GPL article is out of date, here's the working one:

http://www.joomla.org/announcements/team-news/3510-open-source-does-matter.html