I think Macs are quite counterintuitive for people from the Windows world. I jump between:
- OSX (my home box for Lightspeed/iTunes/Squeezecenter)
- KDE3 (my home programming box, and my work desktop until I started using Awesome a few weeks ago)
- Windows XP (my work laptop)
I feel perfectly comfortable jumping between Windows and KDE3. They're basically the same logic, the same way of thinking. OSX, which I'm posting from right now, is entirely different and extremely frustrating for me. To switch to an app, I click on the same icon I used to launch it? The menu bar associated with a window lives at the top of the screen? When I focus different windows, the weird detached menu bar at the top of the screen magically changes? GUI conventions like these don't make any intrinsic sense. You're either used to them or you're not. People who are used to Windows will find the KDE3 conventions quite familiar, whereas OSX will be quite alien.
Customization is a different issue. "End users" aren't likely to sit down at the desk of a customization-mad hacker. They might inadvertently screw up their own desktops, but they can do that with Windows anyway. "My entire screen is gray!" "Where did all my files go? They were here yesterday!" Except with complete computer beginners (a vanishing species) it's a relatively minor problem.