Prism of Inner Calm (http://www.wowhead.com/?item=30621) from Lady Vashj appears to have been buffed by a decent amount (about 250%). Pre-patch it was -54 threat per critical strike. In patch 2.12, it has been changed to -150 threat on each critical strike.

I wanted to throw some quick math into the equation so some of you could understand how much this trinket actually does.

On our last Magtheridon kill, our Enhancement Shaman used 579 melee attacks over the course of 8 minutes. Of those 579 attacks, 180 of them crit. At -150 threat per critical strike, That's 27000 reduced threat over the course of the fight. That's roughly 3375 threat per minute. Keep in mind, his crit is rather low fully raid buffed (about 30%). The higher your crit, the more effective this trinket becomes.

Reference: http://www.lossendil.com/wws/?report=4p3leckiqrudu&a=11

For the all the theory crafters here, What do you guys think of this trinket for the builds that generate tons of aggro, but have no way to wipe threat other than death? Fury Warriors and Enhancement Shamans are the first to come to mind, but I'm sure there are other classes/builds that could benefit just as much.

Math has never been my strong point, so I was wondering what those more mathematically gifted than myself think of this trinket?

You may want to go here: Prism of Inner Calm

hrm, that didn't pop up when I searched. Delete this threat please.