My experience is that when a UI feature is present in OS X and Linux, the OS X version will typically (though not always) be less buggy and more polished.
I've got Ubuntu 12 open in VMWare, running Firefox, and so I can compare it to my Mac running Mountain Lion. I'll pick on window resizing. Here are ways that Ubuntu's window resizing is objectively worse than OS X:
1. The resize edges on the right, left, and bottom are exactly one pixel in extent. They're nearly impossible to hit.
2. When resizing the Firefox window larger on the left/top sides, there's ugly flicker and transient drawing artifacts on the right/bottom side.
3. The resize cursors are misleading. For example, if I grab the top and resize the window as tall as it will go, the cursor still implies it can grow taller. On OS X the cursor changes when the window reaches a limit.
4. An Ubuntu Firefox window can be sized down to three pixels wide. It's hard to click on this window to make it bigger again.
5. Ubuntu allows me to position the window under the launcher and then resize it smaller. Such a window then gets "stuck" behind the launcher. I was also able to get an OS X window stuck behind the Dock, but it was harder: I had to make the Dock smaller, reposition the window, then make the Dock larger again.
6. If you position a window partially offscreen and then try to resize it smaller, it does this weird jitter thing.
7. Ubuntu does not appear to support background, fixed aspect ratio, or centered resizing, which are power-user features in OS X that you can access with modifier keys. If I hold down the shift key, then the Ubuntu window does some sort of snapping thing where it alternates between being as wide as it can, and being three pixels wide (??)
That's from a few minutes of poking around with a single UI interaction.
This isn't a fanboi post. While I like OS X, I noticed things that Ubuntu does better. But in turn, an objective Linux user cannot miss the many things that OS X does better.