Bolstered OS X Inline Previews
To augment the preview features (Quick Look, Cover Flow, basic icon previews) present in Leopard, Apple adds an enhanced inline preview to the Finder’s icon view in Snow Leopard. When you view a folder that uses icons of 64 by 64 pixels or larger, mousing over your files will display preview/playback controls. If you mouse over an audio or video file, you’ll have access to a play button. If you mouse over a Word doc, a PowerPoint presentation, or a PDF (among other common file formats), you’ll get forward and back arrows for paging through a document.