Wow... this crack is small, but it is deep, and may prove harder to mend than to make.
Samba is a keystone project. It is the primary way to achieve interoperability between Linux and Windows systems. By signing on to the GPL 3 bandwagon the Samba team is escalating the growing rift between Linux development camps to a full blown hot war.
A great deal of that growth is due to adoption in the corporate space and financial support in terms of dollars and developers. We have a good thing going when both freelance and commercial developers can contribute to the same shared goal, a stable and free way that everyone could use to replace software that was unreliable, expensive, and strictly closed source.
While the FSF will likely see this decision as a major coup for it's camp, I have my reservations about it's long term impact. As the community that drives the Linux, BSD, and GNU/FSF projects forward grows, commercial players have had an increasingly large role in driving adoption forward.
Numerous commercial solutions have been developed to provide services to windows users from a stable Linux platform. Many of these companies have helped support the ongoing development of Samba. Some of these companies don't have the luxury of switching to GPL 3. Others just don't want to because they view the GPL 3 license as an attack against those that disagree with the FSF's position on free software. Most business owners won't take that risk if the body responsible for stewarding all GPL code is holding a gun to their head and has already pulled the trigger twice (TiVo and Novell).
That argument is tough to counter when your boss is arguing not to open code on a project at all.