You might be familiar with the File > Duplicate (Command-D) command in Finder. New in OS X Lion is the function “Duplicate Exactly”. You can access Duplicate Exactly by pressing Command-Option-Shift keys while in the File menu. The “Duplicate” menu item will change to “Duplicate Exactly”. Or you can just press the keys Command-Option-Shift-D.
When you choose the normal “Duplicate” command, OS X will create a copy of the file and set the file owner to your login account. “Duplicate Exactly” will create a copy of the file but the ownership of the file follows the source, thus ensuring the exact same file even for file permissions.