A further refinement, which I think I like even better, though it's slightly more complex, is to divide s days into two categories: routine lowercase s-days (weekends, vacation days, minor holidays), and really special, rare capital S-days (Christmas, Thanksgivings, your birthday). On the lowercase s days, "sometimes" = "once." On the capital S-days you get complete freedom. I'm not aware that anyone is actually doing this version, but it seems very attractive to me.
This quote is from http://everydaysystems.com/bb/viewtopic.php?p=30447. I am starting to do this and am LOVING it!
My husband works 12-hour shift work, which includes a lot of weekends, so I am still keeping them as S days, but little ones. I need big S days, I think, when S days are SOCIAL occasions. Little S days are for little treats for myself. Just started doing it this weekend and I'm very excited about its potential.
A little S day is meaning, for me, 3 regular nice meals maybe with a thing or two that I might not usually eat, and a yummy dessert after dinner. So far, I don't feel deprived at all! I even felt guilty eating a dessert yesterday because I'm not so used to eating them anymore. But I'll get over that!
To me, feasting seems more natural if done in social situations and not all by myself. (Also, I have a background of occasional binge-eating, and it's harder to do that with other people around than if you're by yourself.)