For the article we are currently writing we need to state something about what is a derivative work and what not. This is a grey area and a hot topic. Here is one article: Are non-GPL loadable Linux drivers really not a problem?. Some more opionions are on the GNU FAQ (Stallman’s view). And I remember a Moglen paper on that issue. Need to look these up. Thanks for letting me know any other pointers to important opinions…