It doesn't matter to me what my pack weight consists of. Whether there are 2 gallons of water in it or just a pint, whenever my pack weighs less than 30 lbs I figure it sits comfortably enough that I don't give the pack weight a lot of thought. I just hike and the pack comes along for the ride.

Above 30 lbs that sense of comfort starts to deteriorate somewhat. Above 35 lbs I am becoming distinctly aware of my pack's weight. Anywhere nearing 40 lbs and hiking starts to turn into trudging.

P.S. I am 5'11" and weigh approx. 160.