Rebuild iPhoto Library
Backup your photo library (~/Pictures/iPhoto Library), then rebuild the iPhoto library by quitting the application if it is open, then launching it while holding down the shift and option keys for iPhoto 4.x or the command and option keys for iPhoto 5.x or later. You will be prompted to rebuild the library.
Remember that Backups are always worth the time. Especially the day you need it.
