When you dual-wield one-handed weapons, all damage is increased by 35%, and your off-hand weapon will deal an additional 35% damage.
Single-Minded Fury is a passive warrior ability learned at level 38 for those with the Fury specialization. It increases the damage done while dual-wielding one-handed weapons.
Patch changes
Patch 4.0.6 (8-Feb-2011): Single-Minded Fury bonus has been increased to 20%, up from 15%.