Amazon - Drop down submenus detect/calculate the direction of the cursor to determine whether to keep displaying a submenu or move on
Github - When you click to focus the search bar the navigation disappears to give you more space.
Google+ - When searching, the page indicator arrow slides from the left side to the top.
/via Vedran Židanik
Facebook iPad app - When tapping a tab that is already open, the content wiggles when the sidebar disappears.
/via Thomas Bogner
Google+ - The fixed black google+ topbar works also as a page up button.
Mac OS X - When searching in the help menu of an app, the menu relevant to the result is pulled down with a blue moving arrow pointing at the menu item.
/via Stephen Litt Belch