Those are really bad ideas, if your machine is connected to the Internet.
Just add a regular user account for folks when they come to visit, and remove it when they leave. That way, they don't have to deal with the left-over trash from the previous 'guest'.
Select the menu: System->Administration->Users and Groups. Click on "Add User" and fill in the short form. Your userid is ready. To get rid of it, select it in the list and click "Delete" (make sure the checkbox is checked to delete their files too).