The small icon in the Get Info window in OS X is useful as an application launcher, too. If you have an application selected in the Get Info window, a double-click on the icon will launch that app. A double-click on a document icon will launch that document's associated application. Finally, a double-click on a folder icon will open a Finder view of that folder.
As always, you can still single-click and cut-and-paste custom icons.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2001033111085337