Not that I'm aware of. NEXT however did release objective-C source code, but AFAIK that never went to court (anyone able to find those details - I can't find them now).

The text of the GPL is release source code. There are a few people who want release source code to be the only way out of any infringement. If a company intentionally violates the GPL that starts to look like a reasonable argument to courts. However if a company takes "enough" effort to not infringe and does anyway a smaller penalty would apply.

If you don't have a license and distributed software, then that is a copyright violation and the author is entitled to damages. Exactly what those are is something the court figures out. However one important piece of evidence is the license was release your source code. Thus lawyers want that additional cover of we knew and decided not to use GPL code, and there are the steps we took to ensure we didn't: since we took effort you shouldn't apply that extreme penalty.

I do know that good faith in other areas has made a difference. Companies have been caught bribing foreign officials before - which is a shut down the company level event (many countries have laws that if you bribe a government anywhere, not just in their country). However because the company could show they made good faith efforts to ensure everyone knew not to bribe this was just the act of a rouge employee.

How real is it? Hard to say. Good lawyers will tell you that putting in some effort to ensure you don't infringe is cheap protection even if the risk is low.