I remember someone last year ran with a hunter; he used the hunter as a main assist. He had tank, hunter + 3 others. Basically he would tank all mobs, got the hunter to target one mob and all the others used the hunter as their /assist target. This meant the tank was free to switch mobs to get aggro and the slaves still targeted the same mob rather than switching with the tank. Obviously you can do this with any class...

Also, he said that the hunter dps was really useful in that, in times when his group got out of control, the hunter would keep shooting without needing to keep pressing keys. He raved about his hunter...