Comment 26 for bug 674138

Good news, other people trying to restore their productivity in the face of Unity global menus have found some ways that might allow you to keep using Unity rather than necessarily switching back to Gnome.
   Uninstall the global menus: sudo apt-get remove appmenu-gtk3 appmenu-gtk appmenu-qt
    Set an environment variable: UBUNTU_MENUPROXY=0

Once global menus are out of the way you can restore focus-follows-mouse.

Of course what we would all like is focus-follows-eye, but until then, focus-follows-mouse will keep you from the RSI-inducing task of clicking back and forth between the applications you're using.

Plus you save all those return mouse trips to the top left of the left-most screen every time you need something on an application menu.