As I was testing the hydration system compatible Osprey Zealot recently (see my review here), Osprey also sent me one of their Hydraulics hydration systems to test too.  I considered combining it into my Zealot review but, as the Hydraulics...

I would say it is for mountain biking, above all the other sports I've tried, where the difference between a well fitting rucksack and one that carries badly will show.  As a rider bounces and shakes along a bumpy trail the pack needs to stay...