I would like to add that OS X implements the lock bit differently than Mac OS 9 or earlier.
In MacOS a locked file means the contents of that file are locked. You can move the file or rename the file, but you can't delete or overwrite the file.
In OS X a locked file behaves like an immutable file in UNIX which was created for some arcane reason. An immutable file can't be moved or renamed, but it's host directory can be moved or renamed. In other words the OS X behavior is insane. You can change the path to the immutable file by changing the name or location of it's host directory, but you can't change it by renaming or moving the file. The end result is if you move a folder containing an immutable file into the Trash, you're kinda screwed.
It's really stupid and I wish more people would tell Apple they prefer the MacOS 9 behavior where you can move and rename a locked file. The OS X behavior doesn't make any sense.