I'd even take this a step further and say Vista/XP gets in the way quite a bit. When I know how to do/use something, I don't need constant reminders to 'Apply' things or to confirm a bunch of operations. Every time I venture into MS land, I seem to get this. When I sit down to a Windows machine it's like, 'sigh'. This isn't to bash MS at all, I think they're necessary in the whole computing ecosystem. However, to me (and this has maybe been reduced since the advent of Vista) they are still a little too nerdy when it comes to OS's.
I used the 'Linux Desktop' for a long time, developing on/in it. I tried to like Gnome, but, yah, it's just a hog. I tried to like KDE, but it was too much like Windows (I think it's prob more stable and is faster than Gnome tho). So when OSX finally was usable I switched and never looked back.
Now where are all these guys? Gnome/Ubuntu - no uptake really. KDE - ditto. Windows - catchup, still a pain to use, still a bunch of money, still the overlords making u activate it. OSX however keeps getting better and more and more people are using it. I don't care about the 'Apple tax' because I think that's a lot of bs. Before I bought my first PowerBook I spent *weeks* looking for a capable Linux laptop. All were junk though which, to me describes the PC industry; a race to the bottom.
I don't think developers can make good GUI software. A developer just wants to get some things done and call it good. A 'professional' ui person want's the experience to be top notch. Like the poster above said "move this button 5px left, make this line #ffffff" - I've had to do that before and my attitude was "fuuuuuck you!". So, I feel I've experienced this first hand.
Now, the Mac/OSX isn't perfect - nothing is - and while I like their hardware/design, I definitely can see through their bullshit screen (which sometimes is worse than MS). But every day I sit down to my terminal or Textmate and start working or start on a task, I get it done with minimal interruption from the OS and with a lot of happiness because things work well and look pretty damn good. Looks are important and if anyone says differently then they should go back to fvwm (even circa '03) and hang out there. Looks DO matter.
My friend and I (also a Linux Desktop developer from way back) talk about the state of Gnome or the like and he's always saying - "yo, they're *still* using the same icons from 8 years ago", and it's true. Not saying for profit computing is the way to go, but money motivates and OSX - especially with Snow Leopard - is now king of the mountain. They're going to have to fuck up royally or some amazing something has to come along.
At this point in my life, I'm tired of garbage (like the machines in the Microsoft laptop commercials) and I don't care about compiling my OS anymore to get that extra 5% of performance. I want a beautiful machine that works and gets out of my way. The Mac pretty much fits that bill.
One last note. For servers (now this is a diff story), I 100% use Linux. For the server market, Linux has it figured out and that's where it will continue to shine.