Solution for the iPhoto 11 bug: A little over a week ago we mentioned the problem of the sudden disappearance of the photo libraries once the catalog update finishes, as long as we come from a previous version of iPhoto.
Due to the large number of users who have had problems with the recent new version of iPhoto, with loss of part or all of their photographic libraries, it has led Apple to release this iPhoto update, 9.0.1.
According to the statement from Apple: "This update solves problems that, in extremely rare cases, could cause data loss when updating a library from a previous version of iPhoto."
Due to its importance, it is recommended that all iPhoto 11 users install this update, since the possibility of losing images is something that has already been recognized even by Apple.
You can download this important update from HERE or from the Software Update option of Mac OS X.
Source: idg.es