The easiest way to see the distortion is to make a grid of squares(in a standard res like 640 or 800) and use it as background stretched. When you are in most resolutions it will still be squares. When you go to 1280x1024 it becomes rectangles instead of boxes. What you are "supposed" to do is resize your monitor controls so that they do appear as boxes. Not every res is supposed to "fill" your monitor(otherwise letterbox resolutions look REALLY funny).
Here's my clever comment