I've tried this. I dropped to about 1100 for two days after a weekend of excess, and it worked, BUT, I was starving the second day and the day after I stopped. (blog posts below)
http://idratherbesittingonthecouch.b...oat-train.html
http://idratherbesittingonthecouch.b...18-1076kg.html
I don't think it's necessarily a terrible idea, but for some people I can see it being a trigger to binge, either from the perceived deprivation or the physical hunger if you dip into starvation mode. However, this is how calorie cycling is proposed to work, with a high day is followed by an ultra-low day. I say, give it a try - if it works it will give you back a sense of control. But, learn from my mistakes, and don't do it for more than one day, and don't drop under 1200 calories. Don't aim to "undo" the damage of the weekend by decreasing your calories by the number of extra calories you ate, but instead see this as using the opportunity you created by increasing your metabolism by over the weekend by following it with an extra low day to kickstart you weightloss again. And if you react badly, don't try it again!
Atoning afterwards does work better for me than attempting to save up calories before hand. Also, my calorie allowance for the weekend is 700calories higher than weekdays, which makes it harder for me to completely destroy my diet with a bad day on the weekend.