One of the changes in Yosemite is that the green maximize button on windows no longer maximizes, but puts the window into full screen mode. For how I work, this is a productivity killer. I don’t see any setting to revert this behaviour. However there is a workaround.
Hold down the Option key when clicking on a window’s green button to maximize. This will take a little time to build a new habit.
Apparently one can also double-click the window’s title bar, which I’m quite happy to see.