iPhoto, OS X Lion: About the "file is locked because you haven't made any changes to it recently" message
In OS X Lion, when you begin editing a photo from your iPhoto Library with Preview as the photo editor, you will receive the following message:
Click the Unlock option in Preview when prompted. After editing the photo, the edited photo appears in your iPhoto Library.
Note: Clicking Duplicate places the edited photo on your desktop (or another location you have selected). The edited version of the photo will not appear in iPhoto.