One of my favorite features in Mac OS X is that certain icons themselves are a “preview” of the file’s contents. A photo’s icon is a tiny version of the photo itself, making browsing through a packed-full folder in the Finder less of a chore than it might be otherwise. A customer came in yesterday wondering why some of his icons showed this preview and others didn’t. I didn’t know the answer at first and began poking around preferences and ‘asking’ Google. This was a great question that had me stumped for a few minutes.
I revisited the “Show View Options” window from the Finder’s View menu and saw what I missed the first time through: a checkbox for “Show icon preview.” With this checked, all icons—not just a random few—were turned into previews. Snow Leopard adds functionality to the icon preview for PDF files. If you resize the icons to something greater than 64 × 64 pixels using the slider at the bottom-right of a Finder window, you can place the pointer over the icon and arrows will appear, allowing you to preview the document page-by-page.