Daz wrote ^^ I guess I just never send food back... I just don't come back.
A couple of stories: my parents recently went to a steakhouse where they eat frequently, and had a terrible meal. Because they have eaten there in the past, they were quite surprised that the quality of the meal on both entrees had declined. The server tried to help, but really didn't offer any substantive change. So my dad wrote a letter to the owner telling him the issue. Dad received a letter back from the owner of the restaurant saying that they had had a change in kitchen staff, and was extrenely apologetic. He sent a gift certificate for a replacement dinner (for two) and also let my dad know that he was really glad for the feedback, rather than losing their business.
I was at G. Michaels with a friend recently, and had a longer than usual wait for my entree-- they got slamed with a party of 16 without a reservation on a Wednesday night. And there was some confusion about my order, although I did eventually get the dish I had ordered. Here's the thing... although it wasn't their usual stellar service, there wasn't any *major* problem, they apologized for the wait, and made sure we were covered for bread and drinks. However, because they felt that we hadn't gotten their best service, they gave us each a free desert.
So here's the moral of the story... I left feeling like the management really cared about how I enjoyed my meal there. It went from a slightly *meh* experience to... wow, they have great service at G. Michaels. And I go back again and again because of it.
So in regard to the situation at Bali: In a case where there is nothing wrong with the dish, but the customer doesn't really care for what it is, or perhaps the description didn't match the product, I would say that a smart restaurant would offer to provide a replacement, but not comp the meal. If there is something wrong with the dish, the restaurant should comp the meal.
I think that's it is acceptable to let wait staff know that you didn't like your meal-- if they don't get feedback, how can they help? But I think a lot of the ettiquette depends on the issue. I don't think it is acceptable to ask for the meal to be taken off your bill, unless there was something wrong with it. However, good restaurants should work to retain customers, and offer a replacement, if the issue is within reason. If they ate the whole thing and then complained... I'd be less concilatory.