Airport security is quite easily the biggest pain since bread didn't come sliced. The 11 inch MacBook Air though is one laptop you don't have to take out of your bag at the xray, making the process a little less annoying. The TSA (Transport Security Administration) has approved of the 11 inch MacBook Air based on its size. While it is definitely still a laptop and not a netbook, the TSA is more worried about how much space the device takes up and labels it as “smaller than a standard-sized laptop”.
There is no hard and fast rule as to what measurement will make the difference between having to 'expose' your device and not having to. iPads and 'anything iPad sized' in general can stay in the bag, according to a TSA representative but the TSA still approves of devices on individual bases.