I assume it would save it to mySQL using AJAX to save without user intervention. It would work kind of like the draft checkbox but no one but you would see the story until you did your own save. You would have one unsaved story slot and as long as there was text in that slot, every time you went to the story editor or submission page, the text there would be displayed by default. Hitting the save/submit or cancel buttons would clear the autosave area.