As you may know, The ALT + TAB key combination is used for swapping windows between one and another on both Linux and Windows systems.
Unity 7 has been recently updated, bringing improvements also for the ALT + TAB Switcher. While keeping the Alt button pressed, inside the switcher, the users can use the mouse to navigate between the windows opened and launched it by left click. The right click opens a preview of the opened window.
When keeping the mouse pointer on the Switcher, the selected application gets highlighted.