IcyCool
First Post
Just a quote for those folks who believe that slashing, piercing, or bludgeoning damage dealt by a spell bypasses damage reduction. This quote doesn't disprove that position, but it is interesting. 
Emphasis mine.

Complete Adventurer said:Invocation of the Knife: Beginning at 2nd level, Daggerspell mages develop a strong mystical connection between their arcane spellcasting abilities and the daggers that they wield. Whenever a daggerspell mage casts an arcane spell that deals energy damage, he can turn half of the damage dealt by the spell into magic slashing damage rather than energy damage. Energy resistance does not apply to this damage, but damage reduction might. This power does not affect a creature's ability to resist the affected spell with a saving throw or spell resistance.
Using this ability does not require an action; its use is part of the action required to cast the affected spell. Only spells with a duration of instantaneous can be modified by this ability.
Emphasis mine.