I still actually prefer bottles and never had any interest in trying a camelback. What changed my mind was running out of water on long brevets. Doing a 200k or more ride when it's ~95 degrees or better outside with long stretches between controls was all the convincing I needed. I remember one ride where I had two 1 liter bottles, a 2 liter camelback, and I stuffed another liter bottle of water in my bag. Not that I actually drank that much, but when it's really hot it helps to have water to pour over yourself, too.