It's not confusing, it does the exact same thing it's always done since the 1980s. The zoom button in Windows is horribly broken though - all it ever does is make the window fill the whole screen! How wasteful!...
Considering the number of complaints though, you'd think Apple would introduce a preference setting, or another button or something. And in fact they have - in 10.7 there's a maximize button in the top right corner...
Except the new button is officially called the "fullscreen" button and to hear some people talk, the existence of the fullscreen mode is a foreboding sign of the coming iPad-ification of OS X...
Apple is seen as a company that cares about simplicity and user experience. If a feature is confusing to many, mostly because the behavior depends on application and window size, we should expect them to refine it. Claiming that such users are "wrong" because it works fine for somebody who has used Mac for the last 20 years completely misses the point.
Considering the number of complaints though, you'd think Apple would introduce a preference setting, or another button or something. And in fact they have - in 10.7 there's a maximize button in the top right corner...
Except the new button is officially called the "fullscreen" button and to hear some people talk, the existence of the fullscreen mode is a foreboding sign of the coming iPad-ification of OS X...
sigh.