Specifically, this means that copyright notice in the MySQL source code files will change from referring to "either version 2 of the License, or (at your option) any later version" to "version 2" only, in the MySQL 5.0 and MySQL 5.1 code bases.
Six years ago in the summer of 2000, when MySQL AB licensed its software under the GPL, our founders David Axmark and Michael Widenius made this choice because the GPL was a license followed and respected by everyone. We have kept to it, because the GPL is the most palatable license, and poses the least friction for our user base.
MySQL has been part of the GPLv3 Committee B advising FSF since the GPLv3 draft was announced in January 2006. For GPLv3, we have seen fantastic improvements and hope for GPLv3 to spread. Even though my activity level as co-chair for Committee B was by far higher in the spring than what it has been in the past few months, MySQL AB continues to work with the FSF for GPLv3 to be the new, widespread license under which Free Software is licensed. However, now, until we get clear and strong indications for the general acceptance of GPLv3 over GPLv2, we feel comfortable with a specific GPLv2 reference in our license.
I have been in contact on the topic with Professor Eben Moglen, General Counsel for the Free Software Foundation, and Chairman of Software Freedom Law Center. He has emailed me:
I appreciate MySQL's thoughtful contribution to the GPLv3 drafting process, showing how a business model and an entire company can be built around Free Software. Looking at recent developments and announcements, I believe MySQL will soon be in a position to see the GPLv3 being adopted over GPLv2 by various Free Software projects.