Following an update last week to fix data loss and corruption, this latest bug fix adds some additional print product options and fixes what Apple calls "overall stability and addresses a number of other minor issues."
The 9.1 update gives users photo calendars back, and adds some holiday card options. The first release of iPhoto '11 about 2 weeks ago caused some users to lose their photo libraries. That issue seems to have quieted down, but many users are very upset about how this new iLife app works. It's good to see Apple jumping on these issues quickly, although this latest iPhoto has been a rough ride for many users.
The update is about 65 MB, and can be downloaded from the Software Update option under the Apple Menu. After you upgrade the app will rescan and update your photo library, so take a deep breath.