Symptom
After editing and saving a photo with an external editor, the thumbnail in iPhoto does not update to show the edits.
Solution
Follow these steps to update the thumbnail:
1. Select the photo that you want to edit.
2. Edit the photo with the external editor application.
3. Save changes.
4. With the photo still selected, click Edit in iPhoto.
5. Click any of the iPhoto edit functions (Red Eye, for example).
6. Choose Undo from the Edit menu.
7. Click Organize.
The thumbnail should now be updated.