Usability feels like a second hand citizen to me, when it comes to things like window management / snapping. I come from a very windows-heavy background, so I appreciate the shell experience provided by OSX, but really hate the ear-flicks of trying to use multiple apps simultaneously, and snapping between them, positioning them, etc, in an OSX world.

To be fair, this could be a training / learn-ability issue that may not be present had I learned OSX first.