My first thought when starting multiboxing was: "I don't wanna do shamans", so I didn't =)
I went 1-60 with 1 palatanka and 4 shadowpriests, it went awesome! But, for more synergy and groupboost venturing into Outlands, I am infact adding a shaman in the mix.
Anyways, just wanted to drop my two cents, and to wish you best of luck!