@Jeff Eaton
"The GPL is explicit about what constitutes a derivative work"

Is it really? Because if it was, I would imagine there'd be a lot less fuss going on, and Matt would have mentioned it in the 2 different interviews he's done on the subject.

But it's not ... and he didn't.

And you neglected the fact that the GPL was specifically written for *compiled* code. Unique code is nearly impossible to create in languages like operational PHP.

Like Beagle said, I would not ever expect a lawsuit over WP and the GPL to ever be decided against those who don't believe themes inherit GPL.