[Otto42]

The GPL has been upheld as a perfectly valid and enforceable license on many occasions. However, in all those cases, this happened via initial injunctions or the like, not in an actual final case itself. Basically, once the license was ruled valid by the judge, it becomes very clear that one side had no case and thus they settled to avoid a protracted suit.

The GPL is well-tested in that respect.

[slantyyz]

I guess the problem, especially in the US, is that no case has gone to judgment. It also doesn't help that certain states show certain biases in interpretation. Notice that a lot of patent cases go to Texas?

My presumption on some of the cases where the GPL has been most successful without going to judgement is that those have been the ones where there is the clearest infringement (i.e., Linksys 'borrowing code' for their routers, etc), i.e., direct copies or only slightly modified versions of the original source.

If it gets far enough, I think it will come down to a layperson's (judge or jury) interpretation (based on lawyer and witness arguments) on whether a theme is like reselling a modified car (i.e., Ruf Turbo - a modified Porsche), or an aftermarket car stereo (i.e., one that reverse engineered an automaker's proprietary connector). Yes, code is intangible, unlike a car, and there are places where my overly simplistic analogy breaks apart, but it's not unheard of to look at it in this manner. A federal judge recently compared mp3 torrent sharing to playing music in a business - not that similar, but in the grand scheme of things, you can see some parallels.