I honestly don't think that taking the weekend off from your diet has to be a bad thing. Eating what you want on the weekends doesn't necessarily mean pigging out on everything you missed during the week. I lost over 80 pounds and did not stick to all of my healthy eating habits on the weekend.
I think that having a couple of meals you love on the weekends is a great motivator. If you're like me, you looooooove food (or certain food) and it's highly unlikely you're going to stay on a diet that does not allow you to eat what you like on a semi regular basis. This is especially the case if you plan to stay healthy for the rest of your life. It's not easy to give up your favorite foods forever, but it's also not very logical to go on a diet, lose the weight you need to, then go back to your old eating habits altogether.
I also think you become discouraged by the guilt you feel when you "break" your diet by giving into your cravings. If this is something that is planned, and done in moderation, it becomes a great motivator. It gives you something to work toward and makes it easier to change your eating habits for the long run.