How long is your commute? Surely a water bottle would be enough. If you are carrying a laptop and some books as well as a full water bladder on your back that's gonna' weigh a fair bit and will make you sweat even more.
I've only used Camelbak, and they are great. BUT (and it's a big one) they are very pricy. I remember checking out a Dawg (one size up from the Blowfish), and it's £80-90.
Options: (1) Go with a lesser-known hydration pack brand - there seem to be more companies offering their own take on it. It'll still cost you a fair amount, but probably less than a CamelBak. (2) Use a courier bag (Timbuk2, Crumpler etc etc) which will be the best option for the laptop. See if you can get one with an internal pocket and rig up a hydration bladder inside. (3) Use a courier bag and bottle.
Commuting? Laptop? Files? then you need panniers and commuting bags (waterproof for when it rains). Then you can use the hydration system of your choice be it bottle or camelbak.
I'm with Nickd on this - back is best for me and also I prefer a hydration system rather than a bottle as there is less opportunity for an unforeseen tumble over pot holes. I have had a look at the cloudwalker and it does appear a little small.
I've got a cloudwalker. I doubt very much whether you'd get a laptop in there. I've used it for commuting to uni with a A4 folder and it was fine but you won't get anything bigger than a 12" laptop in there. Thats without any padding either...