I have not noticed anything different. But then again I am still doing non heroic NR instances cause my toons are not 80 yet. If you have a warrior have him put vigilance on the warlock. This ability transfers 10% of the threat from the target to the warrior. Doing this went a ways to keeping aggro on the warrior.

Also it pays to have an "aggro" reset button. This button is configured differently for each class and put in the same spot. When you hit it, all slave toons drop threat and the tank creates threat. This is one of the advantages of playing a mixed team. You get lots of 'oh shit' buttons.