You know, Daniel, that's a very useful thing to know. I'm still using flash cards I bought years ago, such as an IBM 1GB card I bought for my D60. For some infuriating reason, each card remembers the numbering sequence it's been used to and then seems to transfer that to another camera. I started off with my new 5D with a new 2GB Sandisk; faster than all my other cards. The numbering system was fine till one day I ran out of memory and wacked in the IBM card. When downloading the images, I found to my dismay that the numbering sequence had jumped from around 500 to 8,000. It's caused quite a bit of inconvenience creating separate folders for images that belong in the same group. I have 4 different cards with different but overlapping number sequences.