I found the MM horrible for pretty much any gaming; having to lift your hand off the left button to right-click gets old pretty fast. My hand cramped up after just a single game of DotA (WC3 custom map), and that is really saying something because I don't think that's ever happened to me with any other mouse. Because WoW requires less right-clicking, it wasn't as bad as in DotA, but I still ditched my MM for my iBook trackpad before too long.
I can honestly say it was my worst gaming control experience since the time I had to use a Wacom tablet to play Quake 3.
If you want to play games on your Mac, buy a Razer Pro|Click v1.6 (the white, made-to-match-Mac version of the Razer Diamondback). It's comfortable, precise, and it tracks wonderfully.