Here's my question for the pro-Mac crowd: what about OSX makes it the deal-breaker in your decision? What features can you not replicate elsewhere?
As for the question about free software, there's plenty of free legal software. I'm not running a single piece of paid software on my Fedora 13 install, and it's all legal/properly licensed. This is my primary OS which handles everything I did on OSX. (I have to dual-boot Windows to run 3D CAD software for my engineering work regardless of if OSX or LInux is my primary OS)
I have an iPhone, libpod/GtkPod doesn't sync it. Requires me at least Windows XP in VirtualBox on GNU/Linux.
I'm used to a full-featured shell to run small scripts for convenience and not code it as a program in at least Virtual Basic .Net, that requires me at least a GNU/Linux server distribution running in VBox on Windows.
So, at least I myself need both at the same time, I prefer GNU/Linux with Windows in VirtualBox here, too.
Yes, there is a whole lot of free software, and the idea behind is great. The underlying OS of Mac OS X is free software itself, compatible to GNU/Linux with little effort, which was the deal-maker for me. But there is about 10% "quality software", if you look over to SourceForge, Berlios, FreshMeat - you name it. The rest is either command line only and Mac OS X runs it too, or low quality. On Mac OS X, those 10% high quality apps are mostly available native, or run in X11 (i.e. GIMP). Besides, with Quartz and the whole rattail behind it (Cocoa, CoreGraphics, CoreAnimation, CoreWhatNot), even the the simplest low-quality apps look great, because they use the Apple Human Interface Guidelines at least at some level. This is due to Interface Builder beeing lots more comfortable then Glade or Kdevelop's GUI designer, and it forces you to implement these guidelines, and assists you with it. It takes little effort to make a GUI with the look and feel of an Apple product. Glade lets you drag and drop together what every you want in freedom, it doesn't care about the Gnome Interface Guidelines itself, not that there would not exist such a thing. Mac Developers where kind of sandboxed until 2007, because you coudn't just install Windows on you Mac and run the software there, so there have been very different philosophies and approaches to write software, and still are today.
Besides, in contrast to GNU/Linux, there is software for Mac OS X which you can actually buy, and that boosts software quality when you could theoretically compile most GNU/Linux stuff for Mac OS X. If you want to sell your stuff, it has to be better than your free competitor.
A recent example for me is
ScreenFlow. Ever saw anything near that on GNU/Linux? I only know vnccap and Xvidcap. They do it's job, capture a video off the screen, XVidcap even with audio. Not more, not less. But ScreenFlow is a whole different approach, it's more than just hijacking the video output from X11 and the sound from ALSA.
That are the reasons why I choose Mac OS X over any GNU/Linux distribution (And that's what I used for about 10 years as my primary OS. I started coding in Visual Basic back then, and I was in love with GNU/Linux first time I booted up Redhat 7.3, even though I didn't had any clue about C/C++ or even Bash).
I leave the GNU/Linux vs. Windows argumentation to you, as I don't used it for anything more than iTunes and Internet Explorer over the years. All I see which differs on Vista or 7 from XP is a nicer theme, Preview images in the start menu bar, and redesigned system preferences. I could have missed some über-feature.
And if you need Windows for CAD, you need Windows for CAD.