Had a few games against Aaron's Orgres and I brought out my "current" Call to Arms list and would see how it faired. What I realise is that on the first game (Watcht Tower), the anvil was a huge suprise for Aaron, me being able to charge him in the shooting fase effectivly giving me another move gave me the opportunity to out manouver him. Yes thats right, Dwarfs out manouvering.... Making me pull out a big win on the first game (20-0). But on the second game (Blood and Glory) with Aarons knowledge about the Anvil he now played more carefully, being sure not to expose any flanks and not just running his guys at me. Though a few bad dice rolls also helped him in catching some of me Dwarfs (19-1 for Aaron).
So the thing with the Anvil is that if my oppenent does not know what it does and how powerful it can be, its it will be an up hill battle for him/her, mind you if I dont blow the bloody thing up). But if my oppenent does know how it works, all they need to do is a do a quick readjustment to there tactics and the anvil is an easy work-around.