That being said, I found NetBSD and Darwin (non-MacOS X) to be significantly snappier than any version of OS X I've used to date. I keep going back to OS X, though. Not for snappy interface or any particular need for a software package or because it Just Works. I keep going back because the interface organization and arrangement is intuitive, elegant and (accounting for its limitations) requires fewer keystrokes or mouse-clicks per task to get any given thing done.

I'm lazy. I bought a computer so it would do some work for me. I want to foist as much of that work off onto the computer as reasonably possible. I do not need eye candy or other customizability; it distracts me from my task. I do need to be able to begin and/or close a task in about half as many user-interactions as Windows, or KDE, or Gnome or whatever wm you'd like to name. That's the true power of OS X, in my opinion.

It allows me to Just Work and stays out of my way.