I did the Waking Nightmare quest just a couple weeks ago but I've wondering what you guys did. You'll remember at the end you're given an ultimatum from Vaermina. As Erandur, (the man that has been helping you along through the quest), is beginning a spell to break through the barrier and destroy the staff, Vaermina speaks to you and tries convincing you to kill Erandur and take the Skull of Corruption for yourself. As badly as I wanted that staff I'm a good guy and just couldn't bring myself to kill Erandur. The poor guy has been helping me save the entire town of Dawnstar from Vaermina's grasp so I couldn't just slay him for a unique weapon. The reward for not killing him is you get to keep him as a follower.
My question to you is what did you do? Did you succumb to Vaemina's wishes, kill Erandur, and take the Skull of Corruption for youself, or did you let Erandur destroy the staff and gain him as a trusty follower?
Also, I have another question. If you didn't take the Skull of Corruption, do you still get the achievement where you need to have collected all of the Daedric artifacts?