I was fed up with Vista after only 5 months of using it - that caused me to switch to a Mac.
Now that I've owned my Mac for about a year, everything about it is so much better than Windows ever was.
• Not having to defrag the hard drive JUST to get the machine to run faster.
• OS X's stability, robustness and memory management are years ahead of anything Windows has ever done (thanks to the UNIX underpinnings in OS X.)
• Well-designed user interfaces in just about all of the Mac software I've used so far.
I bought the Mac Pro (overkill for what I use it for) over what would have been a capable machine in an iMac for a few reasons as well:
• I'm used to being able to open my machine and install upgrades - you can't upgrade a hard drive in an iMac without voiding your warranty.
• I don't like All-in-One computers. Apple is great, but they aren't perfect. If the screen dies, I'm out a computer for at least several days, and I can't afford that kind of downtime.
• The Mac Pro is powerful enough that I'm future-proofed for at least the next 3 or 4 years (and I've already owned it for a year....)
• Resale value should be pretty good, and I can afford a new Mac Pro for around the cost of a midrange iMac. (I didn't even pay full price for my Mac, so that's even better.)