Color-less Classic -- A friend at Apple notes that Color Classic users can move the contrast slider bar in the Screen Control Panel all the way to the left, making the screen go pitch black. It would seem that users in that situation are stuck, since they can't see the slider bar any more, but pushing the screen contrast button on the Color Classic's front bezel will bring the screen back up.
Cull Graphics Quickly with Preview
You're faced with a folder full of images, and you need to sort through them, trashing some number and keeping the rest. For a quick way to do that, select them all, and open them in Preview (in Leopard, at least). You'll get a single window with each graphic as an item in the drawer. Use the arrow keys to move from image to image, and when you see one you want to trash, press Command-Delete to move it from its source folder to the Finder's Trash. (Delete by itself just removes the picture from Preview's drawer.)