Now that Unholy is viable for decent DPS in Dragon Soul, and is probably even better than frost for a lot of fights, one can ask if it is really useful to use a spec that includes Anti-Magic Zone (5/1/35) or if it is just better to go for the higher DPS specs like 7/1/33 or 5/3/33.
The Tooltip of Anti-Magic Zone reads: Places a large, stationary Anti-Magic Zone that reduces spell damage done to party or raid members inside it by 75%. The Anti-Magic Zone lasts for 10 sec or until it absorbs (10000 + 2 * AP) spell damage.
At level 85, raid buffed in Heroic Firelands gear, and considering that the proc from Fallen Crusader (+15% Strength) might or might not be up, the maximum theoretical absorb should be between 55-60k spell damage. It doesn’t seem like a lot to say the least… But there is a trick, and a big one! It is actually possible to absorb much more damage, and I will try to explain as simply as possible how it works, when it should be used, and why it is very important to spec into it.