I never dual-boxed but i have played my 5 shamans to 70 and priest/4locks locks to 32..

Shamans are better for everything so far most of all because of tremor totem and grounding totem... We also got to face the fact that most meele now will have aoe meele attacks wich doesnt benefit locks very well!

My priest/4 locks will most likley die in WOTLK at 80 and i will drop it for my warlock...

Why?

Teleport is nearly useless since my priest will be left alone...