I just recently create a DK, went trough all the questing (No quest bugged) until the quest that orders you to use the death gate spell, on this point forward, I have take note of 2 mayor bugs in my game:
1- Death Gate spell works, when taking my character to Archerous, the loading screen its stuck, and never end the loading bar, forcing me to close the game client.
2- Every zone I go, the music and sky its the same as the Dks starting zone (The burning sky and the Scarlet crusade wipe up theme xD), its kinda wierd looking every place with the same sky and music (I love the music in the differents zones in WoW).