The user interface of OS X has many things to commend it. Its click-to-focus function is not one of them.
OS X, by design apparently, lacks a click-through capability. As far as I can tell there is no way to enable it. This generally means that when you click on a window to select it, the window itself will be blissfully unaware of the event. If you want to press a button in an unselected window, you must click once to select the window and once again to press the button.
As far as I can tell (and I could have missed something here), this is designed to prevent you activating some random hideous piece of functionality by accidentally clicking off the edge of the selected window, on the window underneath. However, while in certain somewhat undesirable states of mind, this subtle obstacle can become unimaginably irritating.
But surely Dave, can’t you just get used to double-clicking to press a button in an unselected window?
But I damn well shouldn’t have to! What if you have more than one screen (something that OS X in general handles quite smoothly)? The whole rationale falls to pieces. You have multiple screens so that you can rapidly switch your attention between multiple windows without worrying about the mechanics of the window manager. That’s not to say I haven’t tried getting used to it, but unfortunately OS X provides only a subtle visual distinction between selected and unselected windows. It’s rather counterintuitive to have to modify your actions based on the colour of the buttons in the top-left of the window.
Even if I did get used to it, I’d still be screwed because if you double-click on an unselected window, the window receives a double-click event, not a single-click, and something unwanted is bound to happen. For instance, my text editor (Smultron) lists the currently-open files down the left side of the window. If you single-click on a filename, that file will be displayed. If you double-click, the file will be displayed in a whole new window. That in itself is a perfectly reasonable and useful thing for a text editor to do, IMO, but couple it with OS X’s window management and it can become a headache.
What you actually have to do is click once to select the window, wait a prescribed amount of time, and then click again to do what you wanted to do. Gah…