Over the years, my work style on Unix style systems had come to depend on focus following the mouse, but also, importantly, the focused window NOT coming to the front. Combined with the ability to "push" a window to the bottom of the stack when I'm done with it allows me to have lots of shell windows I can work with simultaneously. I can move the mouse into a partially hidden window, run a command, and then go back to my main window without a lot of fuss. I am constantly frustrated by the inability to push down windows in Windows and OS X, or to interact with a background window. (Yes, some apps on the Mac allow limited interaction without bring the window to the front, but it's not enough for me.) I feel crippled by the weak window controls on Macs and Windows PCs systems. Getting rid of the top window by iconifying it, or by dragging the window I want to the top is NOT the same. Expose on Mac was nice, until they changed it. I suppose I should figure it out again.

I'm sure that if I had learned windowing system on a Mac or Windows PC, I'd find that natural and I'd have developed different work styles. But I've got thirty years of experience with highly flexible window managers and miss these features on less capable systems.

If you're using the mouse, not having focus follows mouse means you have to click twice to activate something in a window without focus, which from my point of view as someone who uses focus-follows-mouse, is pointless and irksome.

When I'm not using the mouse, I change the focus with the keyboard (In my setup, focus follows mouse only when the mouse moves).