I've watched the show a few times. I think super nanny goes into some really out of control families - where any sort of reasonable parenting is pretty much completely missing. Usually there are 3 or 4 children who all scream at the top of their lungs, fight and harm each other, and are basically "out of control" in the sense that their behavior is really unregulated by themselves and by any external factors (be that parenting or wanting to behave well in situations like dinner time or at school or whatever). This is topped off by parents who are equally out of control with screaming, verbal threats that are inconsistent, and physical punishment, parents who are not on the same page in terms of how to cope, and often one parent who basically "checks out" of the situation.
Enter Super Nanny who has, I think, 5 days to bring about major change. I think her approach is an enormous improvement over the status quo for these families. Given the short period of time she pretty much has to teach some concrete behavioral things that the parents can use (e.g. time out). She does seem to try to get the families focused more on noticing the children doing things correctly, improving communication, etc. then on punishment. She seems to me, as another poster noted, to be on the farthest extreme of GD. That said, she seems to (edited for TV of course) bring these families a long ways towards better parenting in a very short period of time.
I have a PhD in psychology and did some family therapy. Frankly, it was extremely challenging and the family was often very aware of the problems but not able to change/take responsibility/etc. It is very hard working with a group of people. So, I really admire what she does.