macosxhints - Merge old iPhoto libraries on CD with iPhoto 5 libraries
If you drag and drop an iPhoto library to a CD, the 'magic XML' file isn't created and iPhoto won't recognize the archived library for importing.
This hint discusses several workarounds, and also digresses into problems with copying OS X symlinks from CD. A finder copy may not handle the symlinks, which are relative symlinks, correctly. Using ditto or archive seems to do the trick.
Good discussion, even if it illustrates the problems with iPhoto. It would help if there was some documentation.