Thanks sotelo.
It's perhaps worth mentioning that setting USM to a large radius like this acts as a form of local contrast enhancement. It's similar to the Clarify filter in PSP and makes the image 'pop' without increasing the overall contrast and losing shadow or highlight detail. It works with the unsharp mask filter in any image editor, and you can alter the intensity of the effect with the Radius and Amount sliders - but be careful about going below a radius of about 15 or you may get sharpening artifacts.