Maijson of Arathor has posted a complaint on (surprise!) the official WoW General Forum. However, unlike most complaints ("Why don't paladins get an epic flying mount quest?") this one is actually interesting. Maijson argues that the mechanic of spell immunity for certain bosses is unfair and annoying for certain classes, particularly mages, balance druids and elemental shamans. After some prodding from my guild's second-in-command, I'll add warlocks to that list.
Basically, spell immunity means that certain classes have to respec or they'll do no damage whatsoever on that fight. Many of the bosses in Molten Core, along with Al'ar, are immune to fire damage. Hydross is immune on and off to frost and nature damage, while Void Reaver is immune to nature.
I'm neither a mage nor a nature damage caster, but as a mutilate rogue, nature immune bosses utterly destroy my damage potential. However, having spent far too many fights being affected by an AOE or chasing after a running boss while the spellcasters sit there and fire away, I can't find that much sympathy in my heart. One of my guildmates suggests that instead of total immunity, elemental bosses instead have super-high resistance to schools of magic, which can be overcome through the use of spell penetration gear. This would require the DPSers to change their gear, but not their spec.
Spellcasters, what do you think about spell immunity? Do you think the mechanism is annoying and unfair, or is it merely the caster counterpart to melee-unfriendly bosses?