Patch 5.3.0 (21-May-2013): Mental Quickness now converts 65% of the Shaman's attack power to spell power, up from 55%.
Patch 5.2.0 (5-Mar-2013): Mental Quickness now lowers the cost of shocks by 90% (still lowers the cost of other "beneficial, instant, damaging and totem spells” by 75%).
Patch 4.3.0 (29-Nov-2011): Mental Quickness has been redesigned. Instead of granting the shaman spell power, Mental Quickness now causes Enhancement shaman spells to behave as though the shaman has spell power equal to 55% of attack power. Enhancement shaman spells no longer benefit from spell power from other sources.
Patch 4.1.0 (26-Apr-2011): Mental Quickness now reduces the mana cost of Spiritwalker's Grace.
Patch 3.0.8 (2009-01-20): Mental Quickness and Static Shock have switched positions in the talent tree.; 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.