I thought the weight would be noticeable, but I quickly got used to it. When I do a short ride without the Camelbak M.U.L.E. 100 oz Hydration Pack, I find myself unconsciously reaching for the drink tube all the time.
When I have the Mule, I drink small amounts on a regular basis. If I have to reach for the water bottle, I don’t drink as often and end up guzzling half a bottle at a time, violating the old “drink before you’re thirsty” rule.
It probably doesn’t make much difference, but the water bladder is, obviously, heavier when it’s full. That means that at the end of the ride, when you are tired, it is as light as it’s gonna get.
It also makes a great cushion when you clip out right and lean left.