Before the recent update of the MBA, the Vaio Z was a far more powerful ultra lightweight. Now, though, that has changed. I need a computer that will run Windows 7 and a number of apps in Fusion's Unity mode, as well as a bunch of OS X apps at the same time. Fusion is a resource hog, especially in Unity mode. Heretofore, the conventional wisdom was that a minimum of 6GB of RAM, preferably 8, were required for the purpose. I have discovered, though that my 13 inch 2.13Ghz 4GB of RAM MBA handles Fusion in Unity mode, several Windows apps, and several more OS X apps as well as my 17 inch Santa Rosa MBP with 6GB of RAM ever did. The secret is clearly the MBA's 256GB of flash memory. Although I now have page outs with the MBA that I didn't experience with the MBP, they don't seem to slow anything down because flash memory is so much faster than are conventional hard drives.
I am also delighted by the new MBA's glass trackpad and 1440 X 900 display. I was also pleased to discover that its screen is dramatically less susceptible to reflections than are screens of stock MBPs and all iPads, which have glass in front of the screen. In this connection, reflections from my iPad have aways made me crazy.