Holy Weapon buffs adds sacred attack to all melee attacks. And it stacks with the Paladin's Holy Weapon toggle to make us mighty powerfull against all mobs weak to holy attacks. :)
mobs that are weak to sacred attack recieve like 20% more damage from physical damage when they are buffed with Holy Weapon. Sword Singers and Paladins also have a toggle skill that works the same. As far as I can tell they do not stack :(, nor does Dance of Light, although some people say regualr hits it is stacked but not crits......but I think it just doesn't stack.
clerics newest to beable to solo 35-40 on the trees in EG, but now you can't nuke them, those same type trees that are part of the lvl 35 quest for clerics you can't nuke them eather, so you have to go all meely on them.
I did a dmg test on shackles in EG, with out HW I did about 40 dmg a hit, with HW I did around 30 more dmg a hit. and thats as a cleric.
But makeing it so you can't nuke the mobs any more sucks.