I never did that quest when it was available and I wish I did.
Seems like it's one of those quests that really shows you are a true Warlock or something.
One can only hope that Blizzard maybe will re-implement these kinds of class quests.
And last did any of you guys do the quest when it was in the game? maybe at 60 even?
http://www.wowhead.com/achievement=2357