Apple released an update to iPhoto 9.3 today, containing a number of bug fixes, including one that could cause iPhoto to freeze when upgrading your photo library.
What’s New in Version 9.3.1
– Addresses a problem during the migration of albums from MobileMe Gallery that may cause photos to be moved from their original events into a new event called “From MobileMe”
– Fixes an issue that in rare cases could cause iPhoto to hang when upgrading libraries
The update weighs in at 599.65 MB, and is available now via the Mac App Store, or through Software Update for users with pre-Mac App Store versions of the software. The update is also available for download directly from Apple.