I tried to burn a backup CD but ran into a problem with the amount of data being written.
When I clicked on Photo Library the info below the library/album window said 840 photos and 606 MB. But after iPhoto 'prepared' the blank CD I inserted for burning, the info panel listed 840 photos and 738 MB - too big for a standard CD.
I first thought this might be due to having some photos appear in multiple albums but remembered that only aliases of the photos are created, not actual file copies.
Does anyone have any ideas on the increase in total size?