> On the Mac if you want to customize the window title bar, you are going to be in for a world of pain. Apple provides no API for customizing things like the title bar on OS X.

That is not really a downside. Why should the title bar be customized by an application? The title bar is used for the window management by providing controls to close, minimize, resize, and move the application window. This behavior should not be customizable by the application at all.