Well we've been hardcore brown baggers for the 7+ years we've been together. Before because we were broke. More recently because I am on a diet (perpetual). If I eat out a lot I gain weight. I am just one of those people, for whom I have to watch my caloric intake and excerise.
But DH is not one of those people. He can eat, drink gallons of soda, not work out at all and still be super skinny and healthy. For example he ate 6 dunkin donuts free from work (because everyone else was on a diet) in one afternoon. Came home and ate dinner to boot.
Anyway though I brown bag because I try to control what goes into my food. Eating out has a lot of grease, lot of butter, extra calories I can't afford (waist-wise). And honestly I'm frugal, I'd rather eat out once a week a nice meal than everyday.
But DH really has been wanting to eat out for lunch. He gets invited a lot and feels as though he wants to go. So we decided to budget $10/week. Think it's reasonable? But we'll stop if he gains weight.