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 vanish 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.

Original post by Michael Rose