Ive started using the camelbak on my road rides. Its still considered a fashion faux pau by roadies but that doesn't stop me.

In the summer - I can carry more fluids than my two bottles. In the winter, I can carry an extra jacket, tights, etc.

In the same fashion--I rode with downtube shifters for the longest time. STI/Ergo levers were a revelation when I finally tried them and my long trusted downtube shifters became a burden. Same thing with the bottles. It's become a burden to reach down and pick up a bottle. I can't drink when both hands are necessary, and my frame has to be polished off of whatever I've been drinking on my last ride. Not so with a hydration system and I also find that I drink much more often when I've got a hydration system readily available. That's good.