Same here. I never notice it moving on the bike, and even out running it has been pretty stable. Though, the full bladder does take up a little more space than I would have hoped. However, I find myself putting food items in the second open-top compartment, and leave the main zippered compartment for clothes and other non-squishables.
Though I do agree I wish it had more smaller pockets! Though, there isn't a lot of selection in the 100oz arena, so I am still happy with this choice.
And I have found that, with my camelback and a small waistpack, I can actually carry enough to be moderately comfortable for a full night out, at least from a minimalist approach. That is, I have shelter (5x7 tarp, which goes in the bag), water (100oz in the bak, plus 27 on the bike if I am on that), warmth (6x8 wool blanket, lashed to the outside), food (I could easily fit 2500 calories worth of high-density food in the camelbak + waistpack). Plus loads of other handy trinkets and such. Yeah, I wouldn't have a tent or a stove or hotdogs or marshmallows, but for about 15lbs of weight I could stay out a full 24 hours and remain dry, warm, hydrated**, and satiated. Yeah, anyone can do that with just about any backpack setup, but the big thing that sets it apart is that this is probably one of the most comfortable and stable ways I could carry this much water, in such a compact package.
**Assuming I am fully hydrated when I set out.