It's all the little things that really add up. Some examples:
- Having an easy keyboard shortcut to create folders (On windows, it's: Alt-N, release alt, hit N, hit F)
- Having the menu bar always at the top. The edges of the screen are the easiest to get to with a mouse, so it's always easy to get to the menu bar
- A search feature that is fast (Don't get me started on searching folders in XP)
- Menu item shortcuts that appear at the right side of the menu, instead of hard to read letter underlines
That's just a few of the little windows annoyances that I deal with daily at work. Add them up, and you get the reason for OS X being as good as it is.