I'm not as concerned without "exactly the same" as much as I am with it just not completely falling apart in IE. In print media I'm not concerned about pixels in the least and I can pretty much always get away with eyeballing ruller measurements, but when working for the screen, even a mistake by one pixel can mean disaster depending on the context (image slices lining up, etc..)

Latest quirk... If you float a block element, negative left margin pixel values seem to get multiplied by 2 in IE 6. I had to use negative relative positioning with an equal negative rightg margin to get around this.

Or why in IE if the div (logo) at the top of http://derekstag.com is offset to the right if it's placed at the top of the markup instead of the bottom. The reason is because that div will actually take on the left margin of the NEXT div (which is the blue part of the page). Even taking into account the broken box model (summing of widths and heights in various properties), I can't come up with a reason for this.