The Tharil'Zun and Wanted: Gath'llzogg quests in Redridge Mountains have horrendous respawn rates. They're both around 10-15 minutes each, and there are typically 3+ groups of players waiting for the kill.
On top of that, Gath'llzogg seems to be bugged. I was in a group that finally got a kill on him and only 2 of the group members received a head from killing him, even though we all have the quest.
