This "copyleft is free (as in freedom)" claim bothers me. Copyleft is not free (as in freedom). Its more like free (but this gun pointed at your temple will shoot if you do not agree with The One True Philosophy). That doesn't sound like freedom to me; more like thinly veiled tyranny. (I suppose this is mostly the fault of the redefinition of a derivative work, but that's a separate issue).
My definition of freedom means that every individual has the right to their own One True Philosophy, whatever that may be. Wanna write your software in the nude (as in publicly)? Be my guest. Wanna write code for Dept. of Defense missiles (which probably should never, ever be public)? Go nuts, IDGAF. Etc, etc.
The GPL is a mistake for software development. I don't mean that just because of what I said above. It's a mistake because of its infectious nature. Whether or not you or I agree (or any reason, it doesn't matter), you must comply. Like a Borg drone, with no freedom. With a non-copyleft licence, any library will still be useful no matter the licence of the software it's linked to (well, except the aforementioned GPL-ed code). See libstdc++ for an example: if it really were vanilla GPL, nobody would use the STL (or at least, not GCC's STL)!
(Written on my Kubuntu workstation).