Sadly, it isn't. At least that means I don't have to spend money. :)
It does look good, and it's amazingly thin and light. However, it's bigger than my 12in PowerBook, and much less functional in many ways.
What makes it completely unbuyable though is the non user replaceable battery. If you are intending to use a laptop seriously for a long period (which considering the price of the MacBook Air, most customers would be), then the battery will wear out eventually.
I've been waiting for computers to have flash based storage for ages. The MacBook Air does finally offer this as an option. Sadly, that option is over 800 pounds more. Which is a staggering price, even by Apple standards.