Here's the situation: you have a mess of Finder windows open, like so--
Now you want to close them. So you either go to the File menu and choose "Close Window" or you click the red button at the top left of the first window... and then you do it again... and again... zzz.
If you really want to close them all hold the Option key when you go to the File menu and you can do it in one shot. See below.
(on the left: the regular File menu. On the right: how it looks when you hold the Option key.)
Bonus: if you hold the Option key and click ANY Finder window's red close button you will close ALL Finder windows. Very nice.
Double Bonus: this Option key technique works isn't specific to the Finder. It also works in Safari, Mail, Microsoft Word (but only if you use the Option-click-the-red-button method-- the Option-click-File/Close method does not work), and Microsoft Excel (same restriction as for Word).
That's three.
