I’ve been using my MacBook Pro for Zbrush 3.1 and it works really smooth, and fast even through a Windows boot.
Right now I only have 2 gigs ram, soon to be 4 gigs. Everything else works great. Maya for OSX runs really fast too. So yes OSX runs awesome for other 3D apps as well, but keep in mind I have one of those fancy brand new MacBooks, not the older Motorola chip.
Also if you want to spend $$$ you can get a top end Quadro FX card put in your Mac Pro desktop through Apple. Also dual quad core chips = really fast. But seriously, unless you are made of money, Mac is overpriced. I’m lucky, because my GF is the MacBook product manager and she has about 10, I just counted, lying around the house. as I type this on a MacBook Air.