I use a Camelbak on my road bike because my long rides take me way out in the boonies, ie, no houses with a water hose, no quick-stop stores, nada! I have a Camelbak Mule (70 oz.) and don't really notice the extra weight. Some ladies here don't like how the pack makes one's back sweaty, but I figure I am going to sweat anyway, so I don't mind. I typically keep water in the pack and put my energy-drink-of-the-day in my bottles. I also like being able to stash my snacks in the pack as well. All in all, a Camelbak works for me.
Four wheels move the body, two wheels move the soul.
2010 Kelson custom/Brooks B17 Imperial
2009 Masi/Terry Damselfly
2004 Specialized Dulce Elite/Terry Damselfly
2003 Gary Fisher Tassajara/unknown saddle
1987 Bridgestone 100/Terry Liberator X