Add the posibility that the user can, for the brush paintop, edit a curve that controls the way that the tablet pressure is translated into size, opacity and darkness. The default is to not use these curves, of course, but giving the user the chance to edit it is a plus (because I get the impression that at max pressure, my tablet seems to give a more discrete and pixelated feel, so with my tablet it is nice that now I can set opacity to 100% at half of the maximum pressure).