I've tried handheld bottles, hip packs and several hydration packs in an attempt to find a comfortable way to carry water and a few essentials on long runs and fast hikes. The Nathan is by far my new favorite. It doesn't bounce, is lightweight, and the front pockets provide immediate access to snacks, lip balm, phone/GPS, etc without having to take off the pack.
Two things make it less than perfect for me. Fisrt, the drinking valve allows air to flow back into the tube unless you keep it in the closed position, and it's not that easy to open/close on the run. I swapped out the hose for one off an old CamelBak with a bite valve-probelem solved. The other nit pick is that this pack only comes in one size. I'm small (5' 2", 102 lbs) with a short torso and the sternum strap goes from just below my bra line at the highest adjustment point to my waist line at the lowest adjustment point. This actually works fine and is amazingly comfortable, with only downside being that it puts the hose clip in a pretty useless spot. Not a huge deal--I just put the hose across my chest and tuck it into the little strap.