I will often click on a gray card with the White Balance Selector to white balance an image. However, if I click on that same gray card multiple times I will get a slightly different result each time, as if it's giving me a reading on a single pixel on the gray card rather than an area. As a parallel in Photoshop, it's like using the "1x1 average" with the eye dropper.
Perhaps it might be nice to give the option of a 3x3 or 5x5 average, or perhaps you could drag the eyedropper over a gray card and it would sample several times over that area.
I figured that an averaged white balance would give a better result rather than a single pixel's white balance.