One of the behaviors that has changed in Preview from Tiger to Leopard is the dragging of thumbnails from the side drawer. In the Tiger version of Preview, dragging a thumbnail out of the drawer would cause it to disappear in a puff of smoke, but the original file wouldn't be touched -- similar to what happens when you drag something out of the Dock. In the Leopard version of Preview, dragging a thumbnail out of the drawer will copy that file to the place where you drag it -- very useful for scrolling through lots of images and picking your favorites.

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