When I click the red X in the window, I expect the Window, and the Application, to exit. On Mac OS X, the application is still running, even though there's no window. This makes it difficult to run multiple copies of the same application. In Windows, or Linux, I can have multiple instances of Visual Studio, KDevelop, whatever... but multiple instances of XCode4? I don't think so. Homey don't play that.
On a PC, to take a screenshot, you press the Print Screen button. If you want a screen shot of a specific window, it's Alt + Print Screen.
On a Mac, it's Command + Shift + 4, followed by the space bar, to take a screen cap of a window. OMG SO INTUITIVE.
On a PC, when something needs to be updated, there's a small icon in the system tray. On a Mac, the Software Update appears and jumps up and down like a Jack Russell terrier on the dock. There's no way to ignore it until later, no, you have to click and specifically cancel the update to put it off, and after a bit... JACK RUSSELL TERRIER TIME!
And the Finder. Let's say I want to delete a file. I select the file, and press delete. What happens? THE DAMN THING JUST BEEPS. No, to delete a file, I have to right click on it, or, if I'm not lucky enough to have a mouse, do the two finger click thing on the touchpad - but not too close, because otherwise it won't work, and select 'Move to Trash'. Again, it's intuitive that if I want to delete a file, I select the file in Finder and press DELETE. Which is the way Windows, Linux, FreeBSD, hell every OS except Mac OS X works.
It's maddening. Mac OS X is absolutely NOT intuitive.