In older versions of Ubuntu when you pressed Ctrl+Alt+L it would lock and blank the screen (start the screensaver). In 14.04 it just locks the screen.
How can I get it to lock AND blank the screen?
Open System Settings and navigate to Keyboard -> Shortcuts. Open the "System" section, click on "Lock screen" and press Backspace. This will disable the system lock screen shortcut.
Now click the
in the "command" field.
Click "Apply". Now click "disabled" next to the shortcut you just created and press the key combination you want to use to lock and blank the screen.