I format my card every time I put it back in the camera. If I've switched between cameras (D70 and D200), I make sure that I format for that camera. That said, if one formats the card while the camera is set to shoot in one mode (JPG vs NEF), does it matter if you then switch and shoot in the other mode? Or is this as dumb as asking whether it makes a difference if your computer writes Word files (.doc) on a disk versus Excel (.xls) ? :redface: I've never switched modes mid-card, but the question came to mind today.