Well, actually, many people have hacked theirs to use black permanent markers (which are etch resistant), so, I don't see any reason why you couldn't use it to

Well, actually, many people have hacked theirs to use black permanent markers (which are etch resistant), so, I don't see any reason why you couldn't use it to black out circuit tracks on PCB's, than simply etch the boards with acid. It isn't quite printing them, but it does make the process much easier!