I've used IBM and Lenovo x-series (x41 and x60) laptops before and while I'm generally a fan and would definitely go with them as my number two choice, I've never had one "Just Work" with Linux. It's always very close, but there is always something. The x-220 was also more expensive for equivalent specs when I bough my Air, especially if you took into account the cost of replacing whatever drive it came with with a 120GB SSD. Also it is slightly larger and slightly heavier than the air, and for me size and weight where a big factor.
Then there are minor things like that there are no stores anywhere around here that sells them, meaning I'd have to buy one without playing with it first. Also it's basically impossible to buy one without a Swedish keyboard layout in Sweden, while Apple will happily let me choose any keyboard layout I want. None of these are deal-breakers in them selves but they're things that kind of add up.
Then there are minor things like that there are no stores anywhere around here that sells them, meaning I'd have to buy one without playing with it first. Also it's basically impossible to buy one without a Swedish keyboard layout in Sweden, while Apple will happily let me choose any keyboard layout I want. None of these are deal-breakers in them selves but they're things that kind of add up.