The gpl-violations.org Legal FAQ answers questions regarding to legal issues and legal action that has been taken by the project.
What damages do you request when a case goes to court ?
From a (German) legal point of view, damages are a totally different issue from the 'cease-and-desist' issue. So in all cases that went to court so far, we've only enforced the latter.
Nevertheless, there is a real damage, and you can put numbers on it. Look at projects such as MySQL or ReiserFS, who are successfully earning money by dual-licensing. So if the particular (infringing) vendor would have negotiated alternate (non-GPL) licensing, the copyright holders could have earned money at the expense of the obligations of the GNU GPL. For the Linux kernel this is not possible, since the copyright is distributed among thousands of individuals, and it's unrealistic that you would make a deal with all of them.
By pointing at those dual licensing business models, I am confident it is possible to counter any of the "you didn't loose money because you gave it away for free" arguments.
Why do you send warning letters to GPL violators without contacting them first?
When we started enforcing the GPL, we tried it by sending e-mails, faxes and letters ourselves, rather than going through lawyers. However, those letters were simply ignored in almost all cases.
Therefore, it is our experience that trying informal means of communication is not worth the effort, especially since it reduces the amount of time we have for applying to a preliminary injunction (in Germany), and therefore puts us into a worse position.
Formal warning notices sent through our lawyers always tend to draw attention at the appropriate management level, and therefore tend to be addressed with the required seriousness for a major copyright violation.