Windows 7's Preview Pane
Windows 7 has an optional preview pane for use in any Explorer window. Select a file, and the preview will appear in the preview pane. Compared to Snow Leopard’s preview feature, Windows 7’s seems pretty basic (text loses all formatting, for example), but it’s better than nothing. Also, as was the case with Vista, folder icons in Windows 7 give you a peek at the folder's contents.