One of the documented changes to the PTR is a change to avoidance in general. Here's the overall text:
- Agility: The amount of agility required per percentage of dodge has been increased by 15%. This change required recalibrating the amount of dodge a player has with 0 agility by a slight amount as well, so all players will see their dodge percentage vary a small amount.
- Dodge Rating: The amount of dodge rating required per percentage of dodge has been increased by 15%. This is before diminishing returns. Combined with other changes, this makes dodge rating and parry rating equally potent before diminishing returns apply.
- Parry Rating: The amount of parry rating required per percentage of parry has been reduced by 8%. This is before diminishing returns. Combined with other changes, this makes dodge rating and parry rating equally potent before diminishing returns apply. Parry still diminishes more quickly than dodge.
Don't freak out.
Here's the thing about being a tank that's based around talents primarily: nerfing stats doesn't hurt nearly as much. As an example, let's take...well, me. I'm not totally Ulduar-geared yet, but I have a good chunk of pieces and have mostly gone for stamina, only using agility when I had a shared piece of gear. I have minimal PvP gear.
Here are my stats currently, raid buffed (courtesy of Rawr):
Dodge Rating: 194
Defense Rating: 91
Avoidance PreDR: 71.102%
Avoidance PostDR: 58.416%
So what will I lose? Effectively I'll lose 15% of that agility and 15% of that dodge rating. That means I lose 268 agility and another 29 dodge rating on average*.
That would mean pre-DR, my avoidance would go down by:
dodge/agility * agility + dodge%/dodge rating * dodge rating
1/41.67 * 268 + 1/39.3 * 29 =
6.43 + .737 = 7.16%.
So a 7.16% dodge rating reduction before diminishing returns. Or a total, Pre-DR value of 63.93% avoidance overall.
What does that mean after diminishing returns? Well, this is 7% dodge at the top, not the bottom - meaning it's getting hit the 'hardest' by DR. But in practice this means all we need to do is in Rawr reduce our stats by the above and see our post-DR results.
And if you do that...the post-DR results are a mighty 46.1% dodge.
So it's about a 4% loss for me, give or take.
Except...Rawr does things like average out procs for an overall dodge value. Which means things like DM:G are counted as having 100 agility instead of 0 some of the times, and 300 other times. Same with Heart of Iron and Mongoose. The long and short of it is that overall dodge rating is going to not decrease quite as much, but the procs are going to be slightly worse than they were before overall.
In any case, 4% dodge is not really wonderful to lose, but it's definitely not a huge deal. It should bring druid overall damage closer to inline with paladins and warriors, though druids will still take the least amount of damage per hit without cooldowns coming into play. And for the most part, you'll not notice it.
If you're curious about the other tanks, because of the parry change DKs almost are unchanged in terms of raw avoidance (they gain parry and lose dodge), and warriors and paladins lose a small amount (about 1-2 % depending on how they geared).