This article is from the Training Your Dog FAQ, posted to rec.pets.dogs newsgroup. Maintained by Cindy Tittle Moore with numerous contributions by others.
The use of food in training dogs has a long and contentious history. Many people dislike the use of food, feeling that a dog should do things because YOU ask him to, not in hope of a reward. They point to dogs that will refuse to do things when they know they won't get food for it. Others advocate the use of food in training, saying that for many dogs it is the best reward to use, that the use of food is a much more humane method of teaching dogs, and that it is an excellent way to motivate a dog.
Certainly each side has some valid points. For example, the repeated use of food as a _bribe_ will quite often result in the dog refusing to do the expected exercise without the bribe being held out. However, this is considered and incorrect usage of food by food advocates. There is a difference between _bribing_ with food and _rewarding_ with food. Under the latter system, the dog never knows whether or not it will get food as a result of performing the exercise; the rules of variable reinforcement mean that the dog will try harder and harder for that reward. The problem is that many folks don't know how to reward intermittently, and it's also true that rewards are more frequent while the dog is learning the exercise and taper off when the dog understands it. Many people fail to notice the dog's progress, and fall into habits, and hence into bribery.
On the other hand, not every dog becomes an enthusiastic performer for verbal praise or toys along. With some exceptions, almost every dog will view food as a good reward and modify his behavior accordingly to get more of it.
The controversy is really rooted in more philosophical considerations than in actual performance (or not) from the use (or not) of food. Some people just plain don't like the idea of rewarding with food, and others do not mind using it.
The bottom line is that, food or not, most dogs need a reward, a motivator, in order to put on their best effort in training. And the trainer needs to understand (and observe) how to apply the reward most effectively.