I recently acquired an 11.6" MacBook Air (MBA). Weighing in at just over 1 kilogram (2.3 pounds) this is a fully functioning Mac capable of running heavyweight software such as Aperture. It is not a netbook lookalike.
It is missing some functionality, however. No optical drive! No Firewire! No mechanical hard drive! No ethernet port! Instead it uses wi-fi to load software, the two USB ports provide fast access to the solid state drive (128BG) which itself is way faster than a conventional mechanical hard drive. And an ethernet/USB dongle is available should you need one.
The processor speed is relatively slow but as noted above, disk access more than compensates. And the same SSD provides almost instant wake up from sleep mode. Even booting up is much faster.
The fear I had was that the lack of an optical drive would be a problem. It isn't, particularly from the perspective of future software purchases. First, the MBA can "borrow" an optical drive from another Mac or PC. Software loading takes a little longer but the advantage of course is that I do not have to carry the extra weight if a drive around with me. But now the Mac App Store has arrived and the delivery of most Mac software will be through an iTunes style download system. Some software prices have come down considerably (Aperture from $200 to $80, for example) and the ease of buying and updating could not be better.
In short, this is the personal computer concept for the future. Well done, Apple!