The absolute maximum should be 25 percent of your body weight.

12 pounds ain't nothing <img src="/images/graemlins/laugh.gif" alt="" />

You BOB should be a balance between fuction and ability to safely travel over moderately rough terrain. Some may be able to carry 80lbs or more of gear safely while other's may be limited to much less. Practice with you loadout, a pack that you thought fit and rode well in the store you may be willing to throw off a clift after 10 miles of hiking.

Your goal should be the lightest fuctional kit possible... save weight on gear you have more room for food and water. Remember the truism, you can buy cheap and light equipment, cheap and durable equipment, but you can't buy cheap durable equipment... it just doesn't exsist!

In AZ, you're right, 6 quarts isn't much. But in VT, when you have a hard time walking five miles and not finding at least a stream, people look at you funny. :P

Yes, this I know <img src="/images/graemlins/laugh.gif" alt="" />... Growing up in VT I can remember carrying only 2 1L Nalgene bottles and an empty 2L dromedary bag the nights when hking the long trail... Today in AZ, I wouldn't dare do a similar trip without 2 x 3L hydration bladders and a Nalgene bottle <img src="/images/graemlins/laugh.gif" alt="" /> It was quite a paradigm shif for this Vermont Boy!

That's right, I'd forgotten you grew up around the lake. And I think a 72oz bladder and four nalgenes is going light- my dream is Rt 2 from Burlington to St. Jay on foot without having to stop for anything other than sleep and needing only light and oxygen from outside of my pack. But that's just dreaming, and I know it. Heck, I'm just happy I can make room for two days of water (optimistic estimate, probably a day and half) in BOB.

75% body wieght, for me that equates to nearly 95 pounds. and i can carry it. but then again i train every day with a 20 pound backpack(my EDC) and combat boots. also i live in a pretty flat area, so the main problem for me is clearing out to a suitable flood proof ground in a county with the lowest high point and lowest low point, takes some moving.
the things to take into acount are, 1 ground type, lighter loads for rougher ground, 2 weather, less kit needed in hotter climates, 3 how much can you carry, and not just round the garden, 4 BOV ie are you going out in a rover 25 or an army 7.5 ton truck? and also the ground its going out in(ie trucks and mountains don't mix) 7.5 ton trucks can take a lot of stuff, a rover 25 has a smaller boot than my bergen.