‘When it comes to takeovers and valuations, I think the role of GPL as a strategic weapon is often under appreciated.’
I would like to suggest an alternative, and more important, strategic weapn: trademarks. MySQL was purchased for $1 billion because it is a very well known and successful trademark; how can you miss by being the ‘M’ in LAMP. JBoss consistently protected their trademark and was purchased for $350 million by RedHat. Sun knows the value of good trademarks and their protection of OpenSolaris is causing problems in that community. However, there are also examples of non-gpl licensed project and companies: Sleepycat was purchased by Oracle, Zimbra by Yahoo, although still independent SpringSource is doing very well with their Apache licensed Spring project.
GPL is a fine license but is not the secret for success. Having a well known, protected trademark is what really drives success. Owning the trademark to a project allows that company to leverage it for profit; to the exclusion of others.
How do you develop a strong trademark? Start with great technology and a development/support team that is passionate about building a community. The choice of license is secondary.