Having been on the maintainer side of a popular project once before, I've pretty much just taken the mindset of "if you owe them nothing, then they owe you nothing". Basically, pay them, or stop making demands (though suggestions and bug reports are usually welcome by maintainers).
Incidentally, this is why I didn't accept donations for that project (though I have nothing against donations in general, of course). I didn't want to even feel a sense of responsibility to maintain a project I knew I'd eventually burn out from.