Matt Asay today switched his license alliegiance, to Apache from the GPL.
Before anyone starts in with the Arlen Specter jokes, let me say that based on the criteria he sets out, adoption, his argument makes sense. (I also think Matt is better-looking than Specter, at right, from his own Web site, no matter what party you belong to.)
Once an open source product is released into the market, users don't really care what license it uses.
If you are looking to businesses to fund further development, a good argument can be made for Apache or even the Eclipse license. Google likes Apache, IBM Eclipse, and your user-in-the-street could probably care less.
What counts on this question for me is not adoption but development.
If your company wants to release its own code, and control that code, if open source is mainly a marketing concept to you, then a BSD license such as Apache or Eclipse makes perfect sense.
On the other hand, if you're looking for a community to extend your code, to build your code, and to defend your code with their bug fixes and forum support, then the GPL works best.
Communities develop best where rights and responsibilities are equal. But business and democracy are two different things. Business exists to exploit code for profit. Communities seek to exploit code for the shared benefit of all.
I think it's possible that, over the last few years, many companies confused corporate projects with community projects. They made noises about community support, and supporting the community, but they were really in it for themselves, this was obvious to everyone, and besides their code wasn't terribly exciting to anyone other than business allies.
On the other hand many companies have proven you can make a lot of money from the GPL. If you're willing to really embrace the community you create, to nurture that community, and to take no more from the community than the community feels is your due.
Some are finding that a rather big if. It is this if that caused the open source movement to break away from Stallman and his FOSS advocates a decade ago. And that basic, ideological divide remains.
To my way of thinking Matt just figured out which side he was on all along.