Another cool feature has been introducted to Gmail. Now you can see multiple inboxes at the same time. These will appear side by side in place of the earlier one. After you turn on Multiple Inboxes from the Labs tab under Settings, you can configure what you want to see, as well as set the number of messages displayed and the positioning of your panels from the Multiple Inboxes section under Settings.
One thing I have noticed ..this feature doesn't works well with screen resolution 1025x768 or less.Find More Details here : Official Gmail Blog: New in Labs: Multiple Inboxes