OS X has a great user interface. I think Apple spent most of its time developing UI rather than a properly functional apps (read: Garage Band). However there are a few hiccups here and there that may disturb you. Here is my list of top 5 OS X desktop error.
1. No Cut and Paste for file.
Seriously... wtf! It's simple and easy. The only reason that I can find on the internet is "when you cut a file and not pasting it, what happened". And I'm like "really? what the hell!".
2. Alt-Tab to a minimized an application, it wont bring the window up.
If you minimize a window to the dock, and alt-tab to it, it wont pop up like in Windows. Thats extremely annoying especially if you're using double monitor. You'll spend a few moment trying to find out what happened.
3. The Enter function.
In the finder or desktop, pressing enter will let you rename the file. I wouldnt mind that much if every application use that. But no, even for an Apple-Built XCode, the Enter button is to enter the folder, not renaming it.
4. Double Monitor Expose.
I use two monitor with different size and Expose at the top right. Sometimes when I move my mouse to the right to point to the second monitor, the Expose turned on. Its a simple logic error but extremely annoying. My Top Right is on the second monitor, why should I has Expose function on my first monitor.
5. Adjusting application window size.
If you use two monitor like I do, sometimes its very annoying when the first and second monitor dont have the same height. The bottom of the window, which used to resize the window, is below the available viewing. But OS X has a great feature so some apps adjust its height when it was moved to a screen with smaller height. The problem is, not all application has that. Even the Apple-built iTunes does not has that simple but very useful function.