For raiding, I'm about to setup my Druid/Mage combo.

Reason being? I use Healbot, and so I use none of my hotkeys. Those being blank, would make it really easy to play both. Clicking on one hand to heal, nuking with the hotkeys on the other.

I just keep thinking of the difficulties of having to move around in a fight, but possibly for heroics it'd be super easy.