Did you pick up your copy of the latest Journal of Consumer Research? Dude why not? You're behind the times! If you haven't seen it yet, there is an interesting study involving the size of food people order. The study found that people ate more out of a container marked "Small" than they did out of a container that had the same amount but marked "Medium".
It is similar to a study I read about a few years ago involving low fat cookies. People were eating twice as many cookies because they were "low fat". Still a ton of calories, but they thought they were doing good becasue of the label.
Use common sense and your eyes. Just because that soft drink and popcorn are labeled Small at the movie theater doesn't make it a small amount. The "small" popcorn has almost 600 calories and that is the kind without butter!