Patch 5.3.0 (2013-05-21): Now deals 450% weapon damage, up from 375%.
Patch 4.0.1 (2010-10-12): Debuff changed from increasing Nature damage taken to increase chance to be critically hit with chosen abilities. Debuff duration increased from 12 to 15 seconds. Removed charges limit. Now deals 125% weapon damage. No longer regenerates mana through Improved Stormstrike.
Patch 2.0.1 (2006-12-05): With the advent of Dual Wielding, Stormstrike was changed to instantly attack with all equipped weapons.
Patch 1.11.0 (2006-06-19):Prior to patch 1.11, Stormstrike cost 30% of base mana and only reset the swing timer, so that it was only useful as an opener or just after a regular swing. It now acts as described, causing an instant, extra attack.