Mac OS X has coloured buttons on windows: Close, Minimize, Zoom.
Zoom is actually Maximize in most applications but in some basic software like Safari it works as expected: a windowresizer button which resizes the actual window according to its content.
There's a big debate about maximize vs zoom but i think both are important. There are some situation where maximize is much better but elsewhere zoom is more useful.
I was talking about this feature with the creator of the software called DM2
(former DialogMate). With this software you can assign many actions to the Min/Max/Close buttons on Windows (middle/right mouseclick). Unfortunately he abandoned his project.
I think this feature would be very useful on Windows too, do a right click on the Maximize button of a window and have the window resized according to its content. It's like the scrollbars. Their length is determined by the content of the window.
Please somebody tell me if it's a good idea.