The Linux Journal's Doc Searls has published Linux Style: The Laptopia Odyssey, Part 2 in which he compares a 17" PowerBook running OS X to an IBM ThinkPad T40 running Linux.

The PowerBook has been in nearly continuous use since I got it more than a year ago. At home it's hooked up to a second (contiguous) monitor and a host of other peripherals--when it isn't floating around the house, hopping onto one our three Wi-Fi access points. It also travels with me on the road, which is up to half of my time. I doubt many other laptops have seen more use, under more conditions (in cars, on planes, on stages, on laps in less mentionable places), than this one--and that complained less. Which is saying a lot because I've beat the crap out of it.

Also worth reading is Part I - Linux Style: Driving to Laptopia.