The fit and finish of linux desktops, especially KDE, are nowhere near as good as the Mac, and adding a theme which kind of sort of makes it look like OS X only serves to highlight where it doesn't match up.
As a long time Mac user and now Linux user the only desktop which is vaguely tolerable is Elementary OS as at least someone there with a good eye for detail went through and made sure it all fits together.
I beg to differ, but only with the "especially KDE" part. KDE is a different beast than most other modern desktop environments, in that it does not try to mimic OS X style in any way.
KDE was started way back when with a goal of replicating a Windows-like UI, with a Start-menu like launcher and a Start-bar like task bar with applets.
It may not be to your tastes, but the fit and finish of KDE3, 4 and now 5 is excellent. Integrated application sets (K[Anything]) with integration into a centralized control/config panel for shortcuts, MIME type handling, ...
The only problem with this is that other popular applications do not bind this tightly to KDE (understandable from application developers - KDE is not the only game in town).
Previously, GTK applications in particular acted and looked like they were from '93 when run outside of GTK-centric desktop environments (XFCE, Gnome). However, Qt has developed a GTK2 and 3 engine that uses Qt and Qt themes under the hood, largely solving that problem when properly configured (try any stable OpenSuse release, for instance).
And there are bugs and annoying aspects to Aqua, it's not perfect, but it is stable.
Not because you can't, but because the above are better apps and a nicer experience than the Apple equivalents.
Once you get out of Apple's walled garden (and reality distortion field), you might find you like it better.
