I thought Mac owners may find this post of interest. Whilst dragging some picture folders over to MBL I inadvertently dragged the iPhoto folder across to. Boy was that a mistake I don’t wish to repeat again. Although it copied across without incident the MBL wasn’t at all happy. The green light started flashing repeatedly without ceasing for over 48 hours and of course the drive wouldn’t sleep either. In the end I had to send iPhoto to the Trash. Once I had done so the drive immediately settled down again and entered sleep mode.
Unlike your average picture folder iPhoto holds a great deal more, e.g. a database, thumbs, previews, masters etc. - lesson learned.