$1,799 vs. $500 or less
One is the lack of an optical drive. As a fall back, the MacBook Air offers Remote Disc which enables using the optical drives in other Macs and even PC's in the network as if they were attached to the MacBook Air itself. Definitely a cool feature and this led to speculations if a netbook hackintosh like the MSI Wind could possibly use this same technology.
The answer to that is yes, it can. But, as usual, one has to put on his or her geek hat and grab and install this update and then type some command lines in Terminal.
defaults write com.apple.NetworkBrowser EnableODiskBrowsing -bool true
defaults write com.apple.NetworkBrowser ODSSupported -bool true
click here for the original how-to webpage
Relaunch Finder and you get the new "Remote Disc" entry in Sidebar, like so:
Not bad, hey? All I can say is that my MacBook Wind didn't cost as much as the Air and it has three USB ports to boot. :)