Yeah a standard weekly cheat day where you're looking forward to all week is not a good idea. However I think it's actually worse for the mind than for the body. You'll be dieting for the rest of your life and hate 6 days out of 7
I used to find it really hard to stick to primal because I thought I couldn't have carbs, so I wanted to cheat all the time but I now allow myself to eat carbs if they're from healthy sources and I actually have no desire to eat anything non-primal anymore.
That's why I kind of hate to see advice that tells people to eliminate/limit any kind of primal food from their diet. Unless you have a physical issue with some of those foods- fruit, sweet potatoes etc. why avoid them? If you make it too strict, its going to be hard to stay the course for very long.