If you enjoy the three-pane look of a desktop e-mail client, but use Gmail, today is your day. Google just announced a new Labs feature, Preview Pane, allowing you to view and reply to e-mails while navigating your inbox. The feature is also available to Google Apps users.
Once enabled, a new button will appear in the upper right of your inbox. To toggle between the old-fashioned Gmail inbox and the preview pane, click the button on the left.
You also have the option to arrange the preview pane vertically or horizontally, using the drop-down menu on the right.
Google also added a 3-second delay before marking conversations as read; however, you can change that to immediately, 1 second, or never by visiting the general settings.