I think a cheat day really is diffrent for the individual. I alow myself a cheat day every once in a while....but its not every week.....it also depends on what I am doing at the time. Sometimes cheating for me is having and apple, or lite canned fruit in my cottage cheese. I really feel that every once in a while you have to allow yourself something you like to eat. But don't go overboard with it. Say pizza for instance, have a couple of slices....not the whole thing, lol. If you for some reason "cheat" that is not scheduled into your plan....then to extra cardio the next day, or later that same day. Sometimes thats enough to deter you from cheating like that again. lol
For some people, if they don't allow themselves a cheat day.....they will not stick with it and wont achieve their goals. If you want some major results....I would not allow a cheat day for a month or so, specialy if you are just starting. Give your body a chance to get going.