Beth:
The bottom line is that you don't need them. You already have the major weight training series that anyone would recommend (GS, S&H and Pyramids). Within those three, you've pretty much got all your lifting needs covered.
But, that is not to say that PP/SS is not a useful DVD to have. Most people, according to testimony on these forums, use these workouts in the premixes form, rather than "as is." Used "as is," each workout is rather short and doesn't feel all that substantive. But select one of the "do workout twice through" premixes and whoa! It's a completely different ball game for the advanced exerciser.
So, I think it's a useful DVD to have around if there is any chance that at some point in the future you may find yourself taking a leave of absence from lifting and having to stage a comeback! (Let's face it, it can happen to us all, to me quite frequently!) Because, as a beginner/intermediate you can do each workout "as is" and that would be quite enough for one day, thank you. Then, as an advanced exerciser, one of the more substantive, more muscle-exhaustive premixes would be just the ticket for a total body workout when you want to shake things up a little.
Supersets happens to have one of the best soundtracks of any Cathe DVD and I have used it in the past when I was feeling down, knew I needed to exercise, but didn't really feel like it and so chose SS because the music is a total mood lifter.
Hope this helps!
Clare