As a recent Mac owner and long term (8 of them) PC veteran, I feel quite well qualified to be objective here. Having first borrowed a Macbook and then bought a Mac Mini, I've been staggered at the difference in build quality between the PCs I've owned (cheap plastic or badly finished metal) and the Apple hardware (rounded corners, terrific material choices, a feeling of real permanence). Take a £400 Windows laptop and a £800 Macbook and they're patently not the "same piece of hardware".
Of course, the question is: is the better hardware worth a virtual doubling in price? Possibly not, but then there's another factor to consider here, besides the logo(!) Obviously, one device runs Windows Vista and one runs Mac OS Leopard. If it was just down to the bare operating systems then there wouldn't be that much in it, but Leopard comes with iLife 09, including the best video editor in the world, plus the also-staggeringly-easy iWeb, iPhoto and Garage Band, a semi-pro audio studio. Look for similar apps for Windows and you're looking at a few hundred pounds extra, potentially. (And they still wouldn't be as good)
I reckon that add the extra build quality to the extra media software and you get the price difference. Factor in a more robust OS that's not (anywhere near as) prey to viruses and exploits and the buying decision isn't as clear cut as Steve Ballmer say it is.