You may want to change the icon for a file. For example, I have a Terminal file saved, and even though OS X launches that file using Terminal, it gives it an ordinary "white blank paper" icon. Not the end of the world, but just a tad boring. Anyway, changing it is ridiculously simple:
Highlight the file, brings up the Finder menu bar. Select "File : Show Info" (or command-I). The upper left hand corner of the Info box shows the icon, which you can select. This was where I had previously faltered, by double-clicking it, right-clicking it (until I remembered I couldn't right-click anymore), and everything else before giving up. But it turns out that you can copy and paste the selected icon.
So the rest is elementary. Find the application whose icon you want to use (in this case Terminal), and select it. Note that the "File Info" dialog box is global, so every time you select a new widget it will replace the information in the box. Anyway, copy it, select your destination file, make sure the icon is selected, paste -- you're done.
[Editor's note: Yes, this is a very elementary tip. But for those new to the platform, sometimes the simplest of things may not be the most obvious of things. So I've chosen to publish this 'introductory' tip in the interest of possibly helping those new to the platform.
You can also paste just about any graphic image you desire in the box, not just the icon from the originating application. In general, if you can get the image on the clipboard, you should be able to paste it into the icon box.]

