Apple's solutions aren't compatible with Time Machine - it can't be used to back up an external drive and a disk image appears as a single file, meaning the whole image would have to be backed up every time it changes, rather than just the changes.
I currently have my iPhoto library in the /Users/Shared and it sort of works, except for regular permissions issues. I can cope with these OK, but my wife finds them confusing and frustrating.
As a general rule, photos are imported in my account and I manage Events, Faces, Places and PhotoStreams. My wife generally just wants access to the photos to share them and occasionally to create albums.
Is there a better solution, possibly one involving Hazel, Automator and/or AppleScript?
Currently running OS X 10.8.2 and iPhoto '11 (9.4.2).