for me, weight is extremely important. i dislike lugging anything more heavy than it needs to be to get the same work done. the MBA is something i can take anywhere, and it was just what i needed to go in for the AT&T hot spot for iphone; apple makes tethering so much easier to use than winmo ever did. it used to be such a pain in the butt that i rarely, if ever, used it. today with the iphone, and BMA it was totally painless and quirkfree to switch from iphone, to company wireless, and back. and our company network is screwed down tight with RSA security.
my fist day with the MBA was a joy.
wrt screen size; i can work on any size screen as long as the app's i use conform. one of the problems with the hacintoshed mini's were the vertical screen size of 600 or 576 was less than the requirement for certain apps, dialog boxes, and control panels. although there were work arounds for most stuff, garageband for instance, is unworkable on the minis, now so sweet on the MBA :)
after having a healthy selection of cheap-o hackin-mini's it's a pleasure to snuggle up the the 11 inch mac book air. and my belly appreciates the feather light touch, while i'm scanning front row in bed. the old macbook was like a cinder block in comparison.
i also ordered my favorite pattern:
for the lid, and my iphone to match the ipad's pattern. The 11 inch form factor also allows me to keep my nice light weight bag for the MBA + ipad, and accessories.
the nice thing about the mini's though, is i'll always need fixed stations for network, and portables for debugging at home. plus all the ipads when they're too far out of date make excellent performance pads and synths.