it's not allowed by apple and even talking about it on these forums is a no go. i wouldn't be surprised to see this thread locked.
from the sticky thread in the mac software forum.
apple won't let you run OS X on anything other than their own hardware. that won't stop people trying but i would not try it in a corporate environment if you want to keep your job.
quick confirmation found via google:
https://discussions.apple.com/thread/4713808?start=0&tstart=0