Another note on this: When I'm tanking, I like to "warm up" a bit, to see what the DPS is like in the group, before I pull 6-10 mobs at once. If the DPS seems slow to me, I'll adjust my pulls for best survival of the group. If I have two melee DPS and no AOE-types, same deal. (If I have a bard and a black mage, you bet I'm going to pull the entire room if I can get away with it!)
So my first few pulls will seem cautious, but if the group handles them without any issues, I'll get more aggressive.