New Macs play the game just fine under Snow Leopard, no difference whatsoever between the windows version in bootcamp!
If you haven't played the game yet, get a guest license and go for it. You'll see that even if you are not a fan of strategy games, (which believe me, I wasn't), you'll be one in the near future.
I've installed it on my macbook pro and I didn't have any problems. So new iMacs, Macbook Pro's unibodies won't have a problem at all. Good FPS and no difference at all when I've installed it under Windows 7 on the bootcamp partition. So if you don't want to dual boot every time you want to play that game, you don't have to.
Enjoy the game under your Mac OSX.