This new MBA quest for my wife was not intended to replace her high-end 17" MBP which she already has and will be keeping.
She only needed a "lite" version of the 17" MBP for more convenient remote use, where higher storage capacity wasn't necessary, but full Mac functionality in a small and lightweight package was helpful... thus she bought a 13" MBA with 4GB RAM and 128GB SSD for $1120 or so.
Nice little machine which is doing it's job very nicely. It's a good lite-version media-creation machine, bridging the gap between the iPad (for media consumption) and the larger, heavier, fully-loaded 17" MBP (for media creation). For her usage, the three machines each have a good niche and compliment each other well.
I'm tempted by the MBA myself, but don't have as much a need for one. My mobile media consumption machine is an iPad, with a loaded 17" MBP for chair use, and a loaded 27" i7 iMac for desktop use. I am lusting after my wife's new Air, though.