[olov]

I whole-heartedly agree with all of that.

As soon as there is ambiguity there is also legal risk, and attorneys tend to recommend a conservative position. The only way to avoid such ambiguity is to limit yourself to the well proven "crystal clear" GPL use cases. As has been demonstrated in this thread, even those "crystal clear" use cases are often misunderstood by many (proprietary program linking to a GPL library comes to mind).

It helps a lot if the copyright holders clarify their own position, possibly in a license addendum. Like Torvalds did for the Linux kernel (regarding system calls). Now that didn't hinder the whole controversy of proprietary vs GPL kernel modules, of course.

The GPL is tricky.