Take a look at whats inside the MacBook Air, the different chips, really thin display, and how easy it was to take it all apart.
I found this nice pictorial/text guide from Ifixit, showing the relatively simple process of disassembling the MacBook Air.
So just how much do you have when it’s all taken apart?

”
We’re left with 88 screws and lots of parts. It’s hard to believe everything here weighs in at only three pounds.”

http://www.ifixit.com/Guide/First-Look/Mac/MacBook-Air

My personal take on the MacBook Air is that its a really neat idea, but I don’t see it being practical at all.  A laptop without a CD drive?  I mean, I own a 17inch MacBook Pro.  My only complaint about the thing so far is that, well, its too darn big, but I knew that when I chose the 17inch.  I don’t mean its too heavy, or too thick.  It’s just too wide.  And for the occasional train trip, or airplane ride, its not that much of a big deal.  If I actually wanted something smaller and more compact, I’d just buy a MacBook, or get a smaller MacBook Pro.  I mean, the MB is 5 lbs, the MB Air is 3 lbs. . . . .I think most people I know can handle carrying 5 lbs.