The MacBook Air is without doubt a beautiful machine, but a lot of its appeal derives from a canny visual trick: gradually beveled edges. It looks a lot thinner than other ultraportables, but there isn't much difference. The back of the laptop is 0.76" thick, the front after the beveling a quarter inch less.
The screen is actually big enough that the laptop doesn't look small. When the screen stretches 13", as it does with the MacBook Air, you'd want a paper-thin body. But this body is just beveled more subtly. IMO subnotebooks like the Asus Eee look sexier because they're absolutely tiny. (That's not to claim their fit 'n finish is as pretty.)
The MacBook Air's screen is highly reflective, which is painful when you're near a window. Apple doesn't offer a matte screen for this model. The machine's keyboard is chiclet style, and low-profile with little travel and an unsatisfying feel. On CPU, the laptop is pretty but expensive and gutless, like an early PT Cruiser or Mazda Miata.
Buying upgrades from Apple is like getting your car serviced at the dealer: expect a steep markup. On the Air, you pay $300 for a minor CPU speed bump from 1.6 to 1.8 GHz. That's the cost of a whole new Asus Eee subnotebook, a complete 3.0 GHz processor, a 1.5 terabyte hard disk and so on.