You may know that you can expand and collapse Finder folders in a tree view using the left and right arrow keys. But did you know that you can expand or collapse all of the root-level folders at once? It's a cool trick that can save you a lot of time when navigating your Mac's files. With the Finder window focused (click anywhere inside the file view), just type Command-A to select all, then use the left or right arrow to collapse or expand all of the folders simultaneously. Neat, right?
You can also expand a folder recursively (expand all of its child folders) by selecting it and holding down the Option key when you click the triangle next to it (or press the right arrow key when the folder is selected). This works in reverse for collapsing, too. You can also drill down into a folder with Command-Down Arrow, and back up to the parent folder with Command-Up Arrow.
Now, not to blow your mind or anything, but you can combine two of the tricks above: select all (Command-A), and then hold down the Option key while you hit the right arrow key to expand every folder in the view, and every folder inside of those folders, and every folder inside of those folders.... If your hard drive is anything like mine, you just made a fine mess of your Finder window. Normally, you can quickly jump to files in the list by typing the first few letters of their name, but good luck finding anything quickly when all of your folders are expanded. Reverse the process by selecting all and using Option-Left Arrow to restore sanity.
Now, use Command-Space to open Spotlight and enjoy the relief of having the file you were looking for in that folder hierarchy (mess) just appear with a couple of keystrokes!