K.C.
I admit first up that I haven't done potty training yet, so I'm only speaking from advice I've received from trusted friends/relatives, but they all say that punishments never work whereas rewards do. I've been told a thousand times that when it comes time to potty train, I should give tons of praise and encouragement for successes, but treat setbacks and errors as neutral.
I've been told that using punishments does indeed foster the defiant attitude, or worse, make the kid all tense, uptight, and more prone to failure.
Also, one of the reasons we use cloth diapers is because disposables discourage potty training. That's why the disposable companies are now coming out with pull-ups that get cold when wet, because they've realized that kids have no impetus to potty train if they're dry and comfy with super-absorbant diapers. So if you use disposables, perhaps try switching to cloth or at least the disposables that get cold.