I was using vmware fusion running win7 on my macbook but had some serious performance issues. Graphics bugs with the game, DB hanging and getting red performance errors from trinity. I just dug my PC out of my closet and it sits in the corner running db+d3.
I know most people don't use OSX as a vm host, macbook air is probably the farthest thing from a gaming powerhouse, and that you'll get better results with windows, just sharing my experience.