When I first switched from Windows to OS X, I frequently had what I call the "Maximized Window Off by One Pixel" problem.
Since there is no "maximize" button on OS X, I would always manually maximize my browser window. But since humans are imperfect, occasionally I would resize the window 1px from the right edge. When I wanted to scroll down (without using the mouse wheel), I would flick the mouse cursor to the right edge of the screen and "click" to start the scrollbar drag, which of course would click a background window and infuriate the heck out of me. I have since adapted to never use the scrollbar.
Since there is no "maximize" button on OS X, I would always manually maximize my browser window. But since humans are imperfect, occasionally I would resize the window 1px from the right edge. When I wanted to scroll down (without using the mouse wheel), I would flick the mouse cursor to the right edge of the screen and "click" to start the scrollbar drag, which of course would click a background window and infuriate the heck out of me. I have since adapted to never use the scrollbar.