Shoulder Lifters...an explanation
mtbshark,
Here is the skinny on shoulder lifters or "load lifters". First off, they don't lift the load at all, they lift the shoulder straps off of your shoulders so that they don't press downward on your shoulders/trapezious. A more accurate name would be to call the shoulder strap lifters, but load lifter talks about the weight being lifted off of your shoulders since it is now resting on the waist belt instead.
The load lifters consist of a strap that runs from the top of your pack frame (either internal or external frame packs) and connects to the the top/front of your shoulder straps. They only work for you if 1) you have a good waist belt that will support the majority of weight in the pack, and 2) your pack is tall enough to position the end that is attached to the pack ABOVE your shoulders by a couple of inches or more so that they can pull the shoulder strap up a little bit and lift it off of your shoulders. The idea is to use the waist belt to support the weight of the pack and the shoulder straps to keep it snug against your body so that it doesn't fall backwards or move from side to side.
Here is a picture that illustrates what it looks like and the good range of angles for the load lifters. If you look at the pack fitting sections of the major pack manufacturers you will see a more detailed description of what load lifters are and how they work.
So, any discussion of load lifters also illustrates some important aspects of any pack selection. First, each pack is designed for a specific set of purposes and functions. It might be designed as a lightweight day pack, in which case it may not be good for regularly 0hauling out a game animal or be as rugged as you need for your type of hunting. Second, if you are going to be carrying more than say 20# in your pack for any period of time or over varied terrain you will probably want to have a pack with a good waist belt to help carry the weight. And, third, everyone has a different torso length (the distance from the top of your hipbone to the base of your neck, and two people who are the same height can have very different torso lengths, so knowing what your own measurement is important. If you want your load lifters to work you will need to use a pack whose top is above your shoulders by a couple of inches or more. This is why some people get great results from a Blue Widow (they have a shorter torso length) and others think it sucks (they have a longer torso length).
As you research packs you will see that most packs have this issue, that due to their length/height some people think they are great and others think they are terrible. The pack isn't necessarily bad, it just doesn't fit the owner properly.