I run Linux for kernel development - having to load binary drivers is a strict no-no. So 2010 Air with its nVidia chip wasn't really a choice and when I tried nouveau wasn't really stable (still isn't - RE is hard). With 4GB RAM limit on the Air I couldn't run Linux in the VM comfortably.

For the 2011 Air - RAM is still an issue and WiFi card is another one - Broadcom is still working on getting a beta quality OSS driver out.

Compared to that x220 on Linux is very well supported.