All tanks have lost about 30% of their damage in PvP post 3.2 (estimate)
I don't know the exact numbers of the nerf but Pre 3.2, a full STR War had 797 Attack power and 820 with the party buff.
Post 3.2 I now have 637 attack power with the party buff, estimates to around 22% decrease of just attack power.
Now SE has also nerfed our damage bonus, if you don't know what that is pretty much every section (melee/ranged/caster/tank etc) has an increased flat %+ to damage, I estimate they took tanks from 10%+ to 0%.
Here are some before and afters of fell cleave, all under the same, perfect conditions (buffs) Pre and Post 3.2. The difference is about 30%
http://i.imgur.com/j0bcEYb.jpg