The iPhoto library, like any other set of files, can run terrifically when things are good and send you screaming for the hills when things break down. The guys at MacFixIt have posted a useful set of tips in which users can recover their iPhoto files in instances where the library will not load under normal circumstances but also from Apple's Time Machine recovery system.

The article's advice:
Don't move the iPhoto library folder. In cases where the folder is moved out of the default "Pictures" folder and a version of the iPhoto application is upgraded, links can become broken between iPhoto and its library. While it should be easy to search for the iphoto library, it appears that the system treats the library as a system file, and therefore does not include it in Spotlight and Finder searches by default. Therefore, a special search must be done to locate the library and point iPhoto to it. In addition, even if the library can be located, corruption may prevent Time Machine from working properly from within iPhoto, resulting in the same "empty library" behavior in iPhoto.

Possible fixes:

Locate the iphoto library and restore it for "missing" libraries:

In the Finder press the "command-F" keys to open the search window.

Ensure "This Mac" is selected, and that you are searching for "File Name"

In the filters, click the "Kind" menu and select the "System files" option. If "System
Files" is not available, then go to "Other" and search for that filter to add to the list.
With the filter selected, in the second menu select "include".

Finally search for "iPhoto Library" and note it's location.

Open iPhoto with the options key held, and select the iPhoto library from the location you found.

Users can also use Time Machine or other backup files in the Finder to replace "corrupt" libraries with clean copies provided the iPhoto library is in a known location and you believe the library itself it corrupted.

A file called "library6.iphoto" or "library.iphoto" that resides within the "iPhoto Library" package file serves as the catalog for all photos in the library package. Users can restore this file with a working backup file and go from there.

If you've tried this or found your own workaround or fix for iPhoto's library's, let us know in the comments or forums.