If you have access to legal databases like Westlaw/Lexis, you can look up the lawsuits the FSF and SFLC have been a party to. All of those suits were settled and the plaintiffs secure monetary compensation, disclosure of the source code, and in some cases the ability to pre-screen future releases to make sure they're complying with the GPL. The reason why many shops take copyright seriously or ban the use of GPL software (you can argue either way that the latter is or is not a victory for the GPL) is because this creates a deterrent effect.