How does the shoulder turn in the backswing, parallel to the ground or perpendicular to the spine?
Jerry - Jim's right, it depends. What does it depend on? Well, it depends on where you want to be at the top of your backswing. That obviously depends on what you are trying to do in the downswing.
In general, a flatter shoulder turn will give you more "around" and less "up"; it will be more likely to have the club pointing left of target at the top (laid off); it might help you if you are trying to keep a flat left wrist at the top; it might also help if you are "collapsing" at the top as it might shorten up or tighten your backswing a bit.
In general, a steeper shoulder turn will give you more "up" and less "around"; it will be more likely to have the club pointing right of target at the top (across the line); it will be more likely to give you a "soft" or bent left wrist at the top; it might help you to lengthen your backswing a bit.
A lot of folks are too laid off at the top because they over-rotate the left arm flying wedge, and a STEEPER backswing (Soft draw pattern) really helps them.
For me personally, I have a tendency to underrotate the left forearm, and a tendency to collapse at the top (to get the club too close to my head) and especially to get too steep. So I play much better golf with an NSA type backswing - where I'm thinking about turning around my spine and staying very flat.
But a lot of this is about feel and counteracting our (bad) natural tendencies. Thus, many people will try to execute a SD backswing and instead of being across the line, this will put them right on plane at the top. When I think about making a VERY flat backswing, I'm still never really get into a laid off position, because for me the "up" part of the backswing is instinctive. It would take Hank Haney many years of work to get me as laid off as he has Tiger!