Due to a mishap with iPhoto a few years back (NOT casused by user error btw) iPhoto completely erased my camera card before any photos had been transferred to my Mac. Now of course, I always copy the contents of the card before I do any transfers.
If you are ever in the situation where you need to recover the contents of a memory card, you might want to try PhotoRescue. It runs on both Mac and Windows. PC Magazine awarded it 4.5 stars.
