Windfury Totem will increase the haste of both main hand and off hand weapons. It is additive to other temporary enhancements like Sharpening Stones, Wizard Oil, Poisons, or the shaman's own weapon enhancements like Flametongue Weapon.
Before WotLK, this totem used to apply a Windfury Weapon-like enchant on the weapons of nearby party members, offering them a significant burst sometimes when they hit with their weapon, but overwriting any temporary enchants like the ones mentioned above, and therefor was very difficult to use properly.
Does not stack with a Frost Death Knight's Icy Talons or Improved Icy Talons, which are both better.
The casting cost can be reduced with Totemic Focus, and the effect of Windfury Totem can be increased with Improved Windfury Totem.