WotLK spell penetration for shamans?

[DBUndeR]

Hi,
I heard some people in my guild say that spell penetration is bugged here. Having spell penetration would only add a little bit of damage. It isn't possible to fully resist a spell.
Now my question is if this is true? Because a lot of guides here say that you need spell penetration.

[Ironelf]

Get necklace or back piece with 254 Spell Penetration and don't think about it much more :D

It's bugged in a way that polymorph/hex and such 'binary' spells can't be resisted. Only damage ones can be partially resisted (again, not fully, only part of damage). But seriously get spell penetration, with 'default' 97 resistance on enemy you'll do on average around 15% less damage if you don't have spell penetration.