My experience
This is quite the contentious topic. Let me try and tell you my experience. I've been a PC user (and very productive) for many years and didn't understand the passion for macs. I like to think of PC's as Chevy's of 5-10 years ago. If your just looking for transportation, it will fit the bill with known limitations. There are a few dedicated Corvettes.
I've been in the software development business for about 30 years on all kinds of platforms. About 6 months ago, I inherited a MacBook 1,1. I started using it and realized the whole IS greater then the sum of the pieces . I won't go on and on, but will say this: MacOS X is great, and the apps are great, but you will not get the real experience unless you run it on the hardware it was designed to run on. I compare my new MacBook Pro 5,1 to a German BMW M3 in build quality and purpose. It just makes me smile when I use it.
I now have the passion...
-gh