Speaking of applications, the green button almost always works as a toggle between the state the window is currently in and its expanded-so-you-can-see-as-much-of-the-content-as-possible state. For example, if you've resized a Safari window to show just one column of a web page, clicking the green button expands the window up and down as well as to the width of the web page. Click it again and the page returns to its original size. If you've made a Pages document smaller by dragging one of the sides or corners, clicking the green button expands the page so you see as much of its length and width as possible. However, if a page started at its expanded size--say a Keynote presentation--clicking the green button does nothing because its current and expanded size are the same.

But there are exceptions. Click the green button in Mail, iPhoto, iCal and iMovie, for instance, and in each application the window will expand to fill the screen. Do this in iTunes and the iTunes window shrinks down to a mini-player.

If you're the kind of person driven to distraction by inconsistency, the green button's behavior may indeed plant you firmly in the passenger seat. But step back and it makes some sense. The button is designed to show you as much information in a single window as is practical. It just happens that there's a measure of leeway in how that's interpreted and achieved.