I have Windows 8 Pro running OK on my Macbook Air 2011. Installed bootcamp support using Win7 compatibility, and everything works. except....
every so often the trackpad loses scrolling and double click (right clic). I think its related to logging into my domain account which doesn't have local admin privileges on the machine. Or it might be related to connecting to a wireless network, not sure yet. I've seen other reports on this occuring with other versions of windows, so it's probably not a Win8 issue.
I usually use a bluetooth mouse, so I don't normally notice the trackpad issue. Other than that I have no problems and Win8 runs great on my Macbook air. I love it because I travel a lot for work, use Windows during the day at work, OSX in the evening, and I don't have to carry a massive boat anchor laptop anymore!!