I think the reason most people don't take the talent is because in a group PvE scenario, you should never be the one getting hit. If you are, cloak of pain is just an "Oh Crap" button. All the talent would add here is increase your damage output even more, which you don't want to do anyway if you pulled aggro from your tank.
In a PvP scenario, there are just better talents out there, like the immobilize on deadly throw. Where this talent really shines though is solo leveling. I'm using it right now, although I plan to switch away from it when I'm done leveling.