I use a road specific CamelBak. (Rogue) Most roadies do not use CamelBaks simply because most roadies don't use CamelBaks.
I came over from MTB, so I figured I would just use my CamelBak MULE until I got used to the bike. After a little time on the road, I decided to stay with a CamelBak and I got the Rogue.
It has been windtunnel tested and actually improves aerodynamics. I doubt it is any amount that matter to most of us.
Most people that complain about the comfort, have only worn one once or twice. It is one of those things that you get used to, like a helmet, and don't even know it is there. Yes, the cooling thing is true, but you really don't notice after a couple rides.
The weight does not shift at all. It does not throw you off balance. Maybe if you had a 25 gallon one it would.
I have seen two people get carted off in ambulances from going down while drinking out of bottles in the last year.
I have also had to dodge many dropped bottles.
My group ride is huge (100+) and very fast, so this may be a factor of sheer numbers. However, I haven't had to dodge a CamelBak yet.
I like to have my phone, ID, some$$, spare tubes, multi tool and pump in the CamelBak. Not in my jersey pockets, or hanging off of my bike.
I also drink a little more than most when I ride, so two bottles won't do on my long rides. I don't want to stop at a convience store when I ride. If you do go long, the newer Camelbaks are fillable from the outside. You don't have to remove the bladder anymore.
Here is why MTBrs don't use bottles:
It is impossible to use a bottle while going over roots and ruts.
Water bottle nipples??? get covered with mud.
You can get sick from mud (with stagnent water or animal poop in it). Yes, people have gotten e-coli, campolobactor (sp), and other things.
Bottles just won't be there after severe roots or a rock garden.
Bottom line. Do what you are comfortable with. If you stay with a CamelBak, I would highly recommend a road type. The MTB ones do have noticable drag and weight compaired to the Rogue. The Rocket has a plastic frame inside to hold it up off of your back, but it weighs a ton.