Also known as inertia. The reason for a lot of Windows users not willing to switch to a Mac is just a lack of familiarity to it.
I went through this switch almost five years ago. I had used a PC, in some form or another, for about 8 years at that point. I was reluctant to leave the comfort of commodity hardware, but I had just reached the point where I was sick of having to fix things on my computer. My day-job requires a lot of tinkering, and I just wanted a computer that I could work with and rely on without all that extra tinkering.
Probably the biggest reason, though, for the switch, was that I was never really ingrained into the Windows world. My first computer was a Coleco Adam, which taught me a lot about BASIC. My next computer, which I fell in love with, was a Commodore Amiga 500. That computer was just so far ahead of it's time... It was truly a computer for artists, and I still really identify with that. I learned so much on that computer that it's ridiculous. I entered the wider world with BBSes, I learned graphics animation, photo editing, music composition, video game creation, and C programming.
The first PC I bought (a Dell) actually started with OS/2 on it. This was pre-Windows 95, but I tried to keep that thing running for awhile. After eventually moving to Windows 95, I tried BeOS for awhile. That OS had some promise, but just no market share. The file system was brilliant. I then experimented with Linux for awhile, but I couldn't get much past that. There was just too much to tweak with, and I ended up not getting anything else done.
Shortly after OS X 10.0 was released, I took the plunge with an iBook. Now, 5 years later, I don't want to go anywhere else. Things on the Mac just get out of the way and let you get to the work you want to do... I can't explain it much better than that.
To sum it up, I didn't have a lot of inertia, so it was never much of a pain for me. I think change is good, and with computers, you need to be prepared to jump ship whenever a better ship comes along. This is why open data formats are so important. Sink or Swim, baby.
Inspired by daringfireball.net/2006...