Ubuntu 13.10 Session Dialogs
The commands to bring up the log out and shut down dialogs have changed in Ubuntu 13. What used to be gnome-session-save is now gnome-session-quit. LinuxG.net has a summary of the commands. To attach these to a hot key, run System Settings, select Keyboard, and go to the Shortcuts tab. The log out and lock screen hot keys are under System. I set Lock Screen to Ctrl-Alt-L and Log Out to Ctrl-Alt-U. Under Custom Shortcuts, I add Shut Down, and set it to run gnome-session-quit --power-off when Ctrl-Alt-Del is pressed.