the above image is of a macbook air on top of the voodoo envy laptop. at first glance, you may think how amazing apple have been in creating such a thin laptop compared to what most windows based laptop designers can come up with. but in fact, the voodoo is thinner.
from boingboing gadgets:
'Looking at the two, you might parse that that Voodoo was slim and you would register that the Air is also substantially tapered, but you would still probably think that the Envy was one-and-a-half to two times thicker than the Air, as opposed to the reality of being measurably slimmer. And that's why Apple's designers are best of biz: sure, the Envy's designers made it slim, but Apple? They made the Air slim and then they made it an optical illusion for good measure.'
i think this is quite a good point to remember as a designer...
link to boingboing gadgets article