I use a Camelbak Rocket on my road bike on longer rides. Nice padded shoulders. Like Kpicha, I took off the front "boob straps" and it stays on just fine.

For shorter rides under 1.5 hours, I prefer water bottles. Just personal preference - I don't tend to like stuff on my back. I have to admit though, the Rocket is darn comfortable and unobtrusive.

I also pull out the Rocket's bladder (huh...now there's an image) and stuff it into the seat bag of my recumbent on my recumbent days.

bladder holds 72oz, btw. Wide mouth, easy to clean, very convenient.

-j