I wish there were a design guideline on how applications minimize to the system tray. Some applications use the minimize button, some use the close button, and even others have a special button or context menu.
This can be very frustrating when you accidentally use the close button on an app that expects you to use the minimize button. Suddenly the app you thought would be “down there” is closed instead.
My personal opinion is that it should be the minimize button, and there should be an app option that determines whether it goes to the Task Bar or the System Tray. Close means CLOSE not minimize.