A smart folder is a self-updating folder that, in essence, performs a continual, 24/7 search for the criteria you specify. (Smart folders are a lot like smart albums in iPhoto and iTunes, smart mailboxes in Mail, and so on.)

The key to creating one, as it turns out, is the little Save button in the upper-right corner of the Spotlight window when you’ve built a search request (using either tokens or individual criteria rows).

Here’s a common example—one that you can’t replicate in any other operating system. You choose File→Find. You set up the pop-up menus to say “last opened date” and “this week.” You click Save. You name the smart folder something like Current Crises, and you turn on Add to Sidebar (Figure 3-19).

From now on, whenever you click that smart folder, it reveals all the files you’ve worked on in the past week. The great part is that these items’ real locations may be all over the map, scattered around your Mac and your network. But through the magic of the smart folder, they appear as though they’re all in one neat folder.

Figure 3-19. Mac OS X can preserve your search as a smart folder listed in the Sidebar—at least, it can as long as Add to Sidebar is turned on. You can stash a smart folder in your Dock, too, although it doesn’t display a stack of its contents, as normal folders do.