A Command key trick.
While working in a Finder window, you can use the Command key and mouse to learn where the window’s folder resides in the file hierarchy. Just hold down the Command key while clicking on the folder icon in the title bar:

Okay, so maybe you already knew that. But did you know that you can do the same trick in a document window when that document is opened in an application? Command-click the document icon and see the path to its location on disk.

Either way, choosing a folder in the hierarchy opens that folder in the Finder.
Thanks for this tip. Actually, this functionality has been around since way before OS X ever showed up. It was in OS 8 and 9 and possibly in 7 but can’t remember. Its a rarely used feature, but a very handy one. When you need it, you really need it.
Cheers!
This isn’t just a Leopard tip, it works in Tiger as well. Also, there’s a path widget you can put in the Finder toolbar, eliminating the need to click the command key.
Leopard makes it easier by also adding this capability via a control-click, aka, right click, on the window’s title.
That right-click is so handy!
I’m not on Leopard yet, but isn’t there also a Finder preference that shows the path to the current window persistently as a horizontal bar across the top of every window? (I presume that works only in the Finder?)
Yes, it’s called the Path Bar and it’s part of Leopard’s “new” Finder.