Its not a simple thing a lot of emotion on the PC or mac question.  Your right you can get a cheaper PC, and windows.  OS X is a wonderful operating system and still way ahead of windows even vista.  I had to due to funds go from OS X to Vista 64 (OS X is 64 bit).  There are lots of little things that should be there that aren't and the state of freeware while there is lots for windows the quality seemed to be better on OS X.  I would go back in a heart beat (and I will), my wife won't switch off even if she has to delay getting a new system for a few more bucks.  I have programmed and worked on both in lots of different situations.

We could get into viruses, firewalls, spyware on OS X (which really isn't ) to whats steps you have to on windows .  Like anything else its a tool, each has strengths and weaknesses.  Mark B  I believe uses all OS X for his setup.  I will turn this quadcore I have into a renderfarm machine once I get enough funds to get another OS X box.  The OS X the programs are fairly consistent, heck in Vista they took the shortcut for closing a window for an open mail message.  But its one of those things until you use it you don't know what you are missing.  What else besides the 3d do you want to do.