I personally have only been using Macs for about a year, and have been pleasantly surprised. XP for me was/is great, but after using the Mac for a while little things I'd always take for normal OS behavior now niggle me.
Examples: Those little balloons that keep popping up asking if you want to "clean your desktop" and the Windows Key that shoots a sprawling menu up the screen when you hit it accidentally. I now find XP quite intrusive.
Also when I used XP as my main machine I had a huge list of alt xxxx shortcuts in order to get to the special characters, much to my surprise OSX getting say a "é" is just alt e and a "¢" is just alt $ and there are loads more examples of that.
Things like that don't just give a Mac a feeling of being more polished, but actually help my productivity.
Just my 2¢ (or $0.02 for PC users) ;-)
Mac vs Windows, no Real Difference?