It's sometimes been said that the GPL is the best license for building an open source business. The reasoning is straightforward: The GPL has a reciprocal property such that those who embed and distribute GPL software with their products need to open source their software. The practical upshot of the reciprocity is that some companies decide to open source their software and some seek a commercial license so they don't need to open source their software.
At MySQL, a good chunk of the early revenues came from software and appliance companies who decided that while they loved MySQL, they would rather buy a commercial OEM license than convert their own applications to open source. This "Dual License" model helped make MySQL a successful business. We always viewed it as an example of the "quid pro quo" philosophy: If you want to adhere to the GPL and produce open source software, great; that helps increase the pool of open source software. But if you didn't want to open source your software, you can help by funding the development of open source software.
[ Related: Does GPL still matter? | InfoWorld's Savio Rodrigues explains why software vendors tend to stick with GPL. | Stay up to speed with the open source community via InfoWorld's Technology: Open Source newsletter. ]
With the permissive licenses like Apache or BSD, you can do whatever you want with the software without any obligation. There are no implications that software that builds on Apache or BSD needs to be open source. I'm not saying that one license model is better than the other; they have their own strengths and weaknesses.
Matt Asay has recently written that SpringSource's $420 million acquisition may bode well for more use of the Apache license over the GPL:
