I bought this Camelbak Classic, but wish I'd bought another in the Mule line. Its 2.5 Liter listed reservoir seems a LOT smaller than the 3 Liter my old MULE held. Also, this pack is more finicky to seal properly.
I have been doing a lot of mountain biking with my buddies, 50-70 miles with one water bottle cage. I would load 2 to 3 more in my back pockets. Now my pockets can been used for food and other tire supplies make a 4-6 hour mountain bike ride much more plesant.