As the Obama administration works on a new national calorie-labeling law that will supersede the patchwork of state laws already in place—or obviate them, as looks to be the case in my home state of Massachusetts, which passed the law but will likely not implement it in November, as scheduled, while waiting as the new national standards are written—Marion Nestle has a prominent editorial in the June 24 issue of the New England Journal of Medicine. She's honest about the mixed results that initial studies are seeing, and points out how hard it is to find some calorie listings and how meaningless other, enormous ranges are, such as at Chipotle and Cold Stone Creamery.
Still, she's in favor of it, as I am and have said here and here. As she says, if nothing else it gives people a way of understanding calories in the context of food and a daily diet as no amount of advice can:
Despite such logistic problems and modest benefits, calorie labeling is well worth the trouble. Here, at last, is help for explaining the relationship of food energy to body weight. Calories are otherwise impossibly abstract; they cannot be seen, smelled, or tasted. Almost everyone underestimates the number of calories in away-from-home foods, especially when portions are large or the foods are promoted as healthful. Few nonbiochemists understand that "calories" are actually kilocalories, and 1 kcal is the amount of heat needed to raise the temperature of a liter of water from 14.5°C to 15.5°C at 1 atmosphere of pressure. It is much easier to explain how posted calorie counts in fast-food meals fit into a 2000-kcal diet.
Read the whole article (I don't know how long NEJM will keep the entire text available, for one thing), particularly for a quick overview of the context and difficulties of getting the New York law passed in the first place. And then start lobbying your congresspeople to get those regs moving.