i got a 1.6/80 and when looking at macintosh HD, i had 0kbs avaliable. talked to a cs rep for one hour and he finally decided i should swap it. gonna swap it tommorow!
When you have that sort of situation go straight to your local apple store. They should be very accommodating to you as a new MBA owner. They'll probably get someone to look at it asap and if its not something easy to fix they'll give you a new one