While I find that W3C gets it right most of the time, in this particular case, I have to say that IE's box model is superior.
One common issue that I often encounter is when I want to set the width to be a percentage and have a pixel padding as well. To get a div to stretch to 100% and add padding, I am forced to use two divs instead of one - Otherwise applying the 100% on a single div will actually turn out to be more than you expect after the padding is factored in. It makes it really difficult to work with fluid layouts.
