I used a CamelBack Mule on my commutes for over a year but found that I much prefer a rack & pannniers. I can carry much more stuff when needed and the load is at a lower center of gravity than so bike handling is much better. Also, I don't have that big sweaty patch on my back/clothes when I arrive at work. Besides, I don't need that huge water capacity on my 20 mile / 1 hr commute.