Increases your spell power by an amount equal to 50% of your attack power, and reduces the mana cost of your instant spells by 75%.
Now Mental Quickness increases the spell power of the EnhancementShamans based on their attack power, and also reduce the mana cost of its instant spells. This is great for the shock spells.
0300Patch 3.0.8 (2009-01-20): Have switched position with Static Shock in the talent tree. 0300Patch 3.0.8 (2009-01-20): Reduces the mana cost of instant cast Shaman spells by 2/4/6% and increases spell power by an amount equal to 10/20/30% of your attack power. 0200Patch 2.3.0 (13-Nov-2007): Now also increases spell damage and healing equal to 10/20/30% of your attack power.