I bootcamp Win7 on my new macbook air (i7 1.8ghz) and it plays all 1080p video without any problems on the latest k-lite codec pack (using ffdshow). Some airs come with the slower Toshiba SSD which may potentially affect playback. Fortunately I got the quick SSD by Samsung.
http://www.engadget.com/2011/07/25/p...-models-video/