In iPhoto ’08’s thumbnail view, there are a couple of undocumented keyboard shortcuts that make working with thumbnails somewhat easier. If you want to resize the thumbnails, for instance, you don’t have to grab the mouse and drag the slider. Instead, you can cycle between various pre-set thumbnail sizes by pressing 0 (tiny), 3 (small), 2 (medium), and 1 (show one image only). (Previous versions of iPhoto support these same keystrokes, though they offered only three sizes—0, 1, and 2.) When you press 1, you’ll see only one thumbnail at a time, and it will expand to fill the entire viewing area in iPhoto.
While it’s nice to see large views like this, most of the time I prefer to see a number of thumbnails, and not just one. Thanks to a second undocumented shortcut, however, you can have the best of both worlds. First, set the thumbnail size to whatever you like—one of the pre-defined values shown above, or use the slider to set your preferred size.
Next, press the Down Arrow (or use your mouse) to highlight one of the images in thumbnail view, then press the Space Bar. The selected image will now zoom to fill the available image area in iPhoto, just like using the ‘1’ mode above. You can then use the Left and Right Arrows to move from image to image, letting you easily browse a given event’s pictures at a large size. When you’re done, just press the Space Bar again and you’ll then see your thumbnail view, at whatever size you set it up.
I’ve dug through iPhoto’s Getting Started manual, and its list of keyboard shortcuts, and as far as I can tell, neither of these tricks are documented.