I've logged several miles, long days, dusty wipeouts, and brutal hours while lugging around my water, fuel, and other essentials in this pack.
I not only use this for mountain biking, I also use this as my commuter pack. It's got enough space for a couple spare tubes, water, a couple of snacks, and even a change of clothes. I love the insulated hose, because taking a drink on a hot day, and getting a mouthful of hot water - is NOT pleasant.
Also - I'm a very broad shouldered guy, and this pack hits me in all the right places, much better than most hydration packs.