The blog Whole Dog Training has a very nice article about dominance training. A quote from the post:
A study published in the February 2004 issue of the British Journal of Animal Welfare found, “Not only that rewards were more effective in eliciting desired behaviors from the dogs, but that those owners who used punishment-based training had seen a variety of bad behaviors in the their dogs including barking at/aggression towards people and other dogs, fearfulness, excitement, separation anxiety, and inappropriate mounting.” The dogs that were trained exclusively using positive, reward-based methods were significantly more obedient than those dogs trained using either punishment or a combination of rewards and punishment. The authors of the study suggest that “the use of punishment-based training might create a state of anxiety or conflict in the dog that is later expressed as bad behavior.” (Since this study was done, a number of others have also confirmed these findings).
The article also has some great info on dogs being pack animals (not so much). Read the whole article.