In lots of places around your Mac, holding down the Command key while you're clicking on an item will give you info about where it lives rather than opening it. For example, I've mentioned before that Command-clicking a Spotlight result will open it in the Finder.** I also often Command-click a program's icon in my Dock as a quick shortcut to get to my Applications folder. And similarly, Jeff Gamet pointed out that you can Command-click a Finder window's title to get a hierarchical view of where you are in your file system.
One of this feature's most useful implementations, though, is for the things you've accessed recently. If you click on the Apple Menu in the upper-left corner of your screen and choose Recent Items, you've got fast access to recent applications, servers, and documents that you've used.
If you then hold down the Command key before you click on an application or a document, you'll see the menu change, and you'll be given the option to open the item in the Finder instead.
And by the way, I don't really have a text file with world domination plans, no no no. I'm just not that kind of person, you see.
It's actually a Pages file.
**If you're running OS X 10.8.2, you may find that a software bug prevents this from working. I'm hoping Apple fixes this soon, as I use that feature all of the time!