Weight. The number one reason I LOVE the MBA is the low weight and the advantage it is to the mobile user... whether mobile from desk to couch to bed or from office to meeting room to home, its mobility is perfection.
Thinness. The second great quality is how thin it is yet provides a full-sized keyboard and display. The shape makes it feel that it is super thin throughout, so the user is deceived by the "wedge" design to feel ultra thinness.
Performance. The optimization of the Penryn CPU, Nvidia GPU, and SSD are simply amazing together! For the average non-pro user, the MBA will fill faster than a Mac Pro or MacBook Pro!
Quality. The overall quality is shear perfection compared to any other brand. From the industrial design, aluminum case, and overall build quality, the MBA is second to none.
Usage. Looking at a top quality display, having a large trackpad for touch input, and an amazing keyboard second to only the Lenovo Thinkpad's keyboard gives the MBA the best all around user experience when considering the whole package.
For writing, business, academia, mobile professional, light user, and etc, the MBA is incredible. It has everything that I need as is... however, lacks the RAM I really want. But does everything I need to perfection.