Patch 7.1.0 (2016-10-25): Now available at level 40, down from level 44.
Patch 7.0.3 (2016-07-19): Now increases spell damage by 30% (up from 20%) and reduces mana cost by 30% (formerly increased mana cost by 10%). Duration reduced to 10 seconds (down from 15 seconds).
Patch 5.0.4 (2012-08-28): Cooldown reduced to 1.5 minutes, down from 2 minutes.
Patch 3.0.9 (2009-02-10): Now increases damage and mana cost by 20% (down from 30%), cooldown reduced to 2 minutes (down from 3 minutes). Arcane Power and [Presence of Mind] now share a category cooldown. Arcane Power causes a 15 second cooldown. Presence of Mind, once consumed, causes a 1.5 second cooldown.
Patch 1.12.0 (2006-08-22): It is no longer possible to gain the benefit of this spell and [Power Infusion] at the same time by careful timing.
Patch 1.10.2 (2006-05-03): This ability will no longer stack with Power Infusion. If you gain both at the same time, Arcane Power will take precedence.