I've been testing out the mechanics listed in the guide, and I do have to say that improved rend has been a very pleasant surprise, so much that the "Bloody Tank" spec with Improved Rend and Deep Wounds is my favorite protection spec by far. I had a few additional comments.
One thing I've noticed that wasn't mentioned in the guide is the increased 35% rend damage if applied when a mob is above 75%. Placing Rend earlier in the rotation for mobs that die quicker might then be more advantageous, i.e. Shield Slam, Revenge, Rend, Devastate, Devastate etc.
Another observation I had was do you happen to have any thoughts about a quick and dirty prot warrior AOE DPS strategy? Off the top of my head, I'd say something like the usage of Thunderclap, Shockwave (both which activates deep wounds on crit), and Cleave. With the new Cleave Glyph coming shortly (increases affected targets from 2 to 3) that kind of approach may be useful to explain a bit.
Lastly, keep up the good work!
Stay strong. Stay smart. All heart.