Hey man just heading to work here soon and skimming the forums..
Wanted to say I just started a shaman / warrior combo too. I've only ever played a melee class (rogue) and I'm so lost when it comes to how I should be maximizing my levels earned.
This is my first attempt at multiboxing, and I've got them up to 23 atm on Alterac Mountains (Aldoushuxley | Timothyleary).

Anyways, I am also having trouble downing mobs quickly. I don't know if it would be better to spec protection for Warrior and have him generate as much threat as possible for mob focus while I (we) focus on maximizing unhindered dps with our shamans? No idea. Do you think this would be a viable option or does the warrior actually contribute more damage to the equation then I've witnessed so far - have yet to install my damage mod and monitor this.

Sorry if this post seems rushed or nonsensible I haven't slept much xD..