Infoworld poses the question but misses the point entirely.
My guess is if you measure the carbon footprint of notebook X against notebook Y — for manufacture, lifespan, and disposal — you’ll either see there’s a huge difference (where one notebook is from a manufacturer that simply doesn’t care) or they’ll be within a few percent of each other. It’s not like — in hardware terms — Apple has access to secret alien technology.
Unfortunately for PC manufacturers who aren’t Apple, the big difference will be when you divide that carbon footprint by (a) the productivity of that computer’s user multiplied by (b) the likely useful lifetime of that computer. Every study of these subjects (this blog entry links to a few, one of the more recent of many such studies discussed here) shows that Mac users are considerably more productive than their Windows-using counterparts, and that Macs remain in use far longer than Windows PCs (this isn’t hard to prove — check the resale prices for five year old Power Mac G4s on eBay — think you could sell a three year old PC for that much? OK search for Pentium 4 PCs… The omniscient market has spoken. QED). Linux probably fares better than Windows on the second front, but unless “tinkering with the damn thing to try to get videos to play” counts as productivity, not so much on the first.
So while HP, Dell, Lenovo, Sony, Toshiba, ASUStek, Acer et al can try to argue that their latest boxen are 2% more efficiently built than the latest Macbook Pro, they’ll lose out big time (for now and the foreseeable future) on the denominator.