When cycling, I've always been accustomed to wearing a very light and comfortable small backpack with a 2L. Deuter Bladder and room for my valuables. The weight never really bothered me. I prefer this as opposed to bottles because I like to take little sips real often.
But I live in Germany where it's usually cool. Last year on my Sierra Cascade tour it was HOT! I only had the opportunity to shower every 3 to 5 days and I developed sores on my back from the salty sweat under the little backpack.
For this year's NT tour I have a Source Convertube with different adapter caps that fit onto various bottles (PET, Nalgene, etc.)
http://sourceoutdoor.com/hands-on-systems/22-convertube.htmlI use this with a 1L. PET bottle. It seems to me that I have to suck a little harder than when using the same company's valve out of the backpack/bladder, but I'm still very happy with this solution. I still carry the little backpack with an (empty) 2L. bladder inside a pannier, just in case I need to haul large amounts of water. That way the weight (of the water) is positioned low (near the axle).
It's off the subject, but I like being able to easily grab the backpack containing my valuables when I go inside somewhere or for a walk around town and still have my hands free. I personally don't like handlebar bags and carrying any weight up that high.
Happy trails!