Traveling lighter
As a full time graphic designer and photographer, I have been lugging macbook pro around for years and have seriously been ready to chuck it out the hotel window after a week long tethered shoot. The final straw was en-route to Atlanta a couple of weeks ago, the bag with camera, lenses, and computer hit the floor and I thought I was screwed, but amazingly the MBP broke the fall (now 2 mm shorter but still working). I wouldn't have tried to hang the thing, but I was exhausted from lugging around equipment. So, now, with the macbook air, I don't even notice it is there. I didn't migrate, just installed new CS3 and camera shooting software and there's plenty of room for a full week's shooting RAW files. Minor processing done on the road, back ups on passport 250 gig portable USB drive, full processing done when I get back to the slightly crumpled but still perfectly good MBP.
Makes all the sense in the world to me, don't care what it looks like, it feels great!