My understanding from the help file is that the Scale slider on fill styles is supposed to change the effective "size" of the pattern options; as far as I can tell it isn't actually working. Is there some quirk to it I'm unaware of? I move the slider and the pattern does not change at all. Nor does apply make any difference.
Edit: Ah. Apparently, for whatever reason, you have to apply the fill, select it on the map, and then chance the scale. That's certainly counterintuitive.