I am such a loser. It was only by accident that I discovered Smart Folders yesterday. It is a feature of the Finder in Mac OS X that is incredibly clever and useful. And I never even knew it existed…

Smart Folders contain documents grouped together based on search criteria that you define instead of their physical location. Computer file systems are rigid: a file can only be in one folder inside a hierarchy of other folders on your disk. Smart Folders fundamentally change the way you organize your stuff because now a file can literally be in two folders (or many) at once without duplicating or moving the underlying file.

Like Smart Playlists in iTunes, Smart Folders automatically update in real time when you add or remove documents from your Mac. They can contain documents from anywhere in your home directory and external drives, and creating one is as easy as saving a search in the Finder.

The keyboard shortcut for it is Cmd-Alt-N, or you can create them from a search in Spotlight too.