As the author of a book on obesity (The Hungry Gene) I cannot resist responding to Ed's observation that restaurant goers tend to order unhealthy items when said items are coupled with healthy items--like side salads. I do not agree with Dan, that no one goes to restaurants for "healthy food"---anyone who has lived in New York City for any length of time knows that many people stay slim and healthy while almost never cooking for themselves. Some of us do seek out healthy alternatives in restaurants--which is one reason why sushi's popularity threatens the future of certain fish species. People eat sushi--and pay a high price for it--because they enjoy it, AND because it is relatively low in calories.
Science has shown us that biology explains why some of us are more inclined to overeat in a given environment than are others. It's not the "unhealthy" offering that's the problem, it's our response to it. Some of us eat the WHOLE THING, and some of us call for a doggie bag. Some of us "save up" calories for the Big Restaurant meal, and some of us do not. Depending on our inborn tendency to overeat or not, some of us are better off avoiding restaurants--but many of us can enjoy them with relative impunity.
One thing to keep in mind--starch and fat are cheap. This explains why a Grand Slam breakfast at Denny's costs so little--it has pancakes and corn syrup topping and bacon and eggs and toast slathered with margerine--but no juice or fruit or slices of tomato. Healthy, low calorie foods TEND to cost a bit more... So when mulling over a restaurant menu, try to balance cost with health concerns.