Originally Posted by
Sidonis
Affliction > Spriest > Boomkin/Destruction > Demo/Fire/Ele > Arcane/Frost*
That's highest to lowest on the value of Nibelung. They -do- proc off DoT spell ticks, just not DoTs caused by other spells (i.e. it can proc off Haunt, CoA, Corruption, Immolate, SW:P, Devouring Plague, Vampiric Touch, Moonfire, Insect Swarm, Living Bomb, Flame Shock, but -not- off of Ignite, the DoT applied by Conflagrate, or the Languish DoT applied by Boomkin 4pc T10.), for spells like Mind Flay and Arcane Missiles it has a chance to proc off the initial cast, but not the following ticks. It -can- proc off each jump of Chain Lightning, as well as Overload procs.
* The ranking for Frost is for single target DPS, AoE'ing on trash with imp blizzard seems to proc them like crazy.
Basically because of a lack of either hit, crit, or haste on the staff, the general rule of thumb is that it's value doesn't truly shine until you've capped those stats elsewhere on your gear, which is part of what makes it less and less useful the less DoTs you're capable of debuffing a boss with.