I know there's not much new here, but I am amazed that Ubuntu, Linux Mint and friends ship with a Guest account present and enabled. The Guest account is surreptitiously added through a lightdm configuration file, and is not part of the standard user database. Because its not part of the standard user database, it can't be disabled through /etc/shadow, nor disable it through familiar tools such as userdel and usermod. Additionally, the damn account does not show up in distribution provided tools such as User Accounts applet.