Thinner = Smaller
Footprint is not the same as dimensions. Carry it around in a bag, as designed, and it takes up significantly less space than a MB. Hence 'ultra-portable'.
The only dimension in which it's smaller is height -- it's about the same as a normal MacBook otherwise.
It's not even that light, considering what it omits.
There's plenty of people, some of whom have posted on this negative agenda-driven thread, with significant experience using an MBA for highly intensive 'Pro' applications, and have no complaints whatsoever, quite the opposite.
Indeed. I'm one of those folks. I tried using an MBA for about two weeks, and found it totally unsuitable.
There was too little space on the drive, HD performance wasn't that great, it didn't save any space in my bag, it ran quite hot indeed, and to top it off it lacked many of the ports I would have expected on a $1500 laptop.
I could've lived with those limitations though, if it offered me savings in terms of weight, or better performance, or longer battery life than competing laptops. Problem is, it didn't.
I'm not saying it's not a decent laptop for some folks -- I'm sure it is -- but trying to claim that it's an ultraportable (a category occupied by < 3lbs, small form-factor subnotebooks) is a little silly.
Anyway a netbook will be nothing like an MBA. It will be the natural evolution of the existing Mac netbook.....i.e. a hypertophied iPhone/Touch, with maybe an 8-inch touchscreen and an Atom CPU, probably runnning a cut-down OS X. Carbon fibre casing too.
I dunno... I have a feeling that Apple would want to use their "netbook" (if they were to make one) as a transition product -- a cheap, but capable device meant to move PC users from their iPhone over to a Mac. Running a crippled OS X wouldn't really achieve that -- but a full version of OS X might just be enough of a "taste" for most users to persuade them to make their next desktop (read: high margin) purchase from Apple.