As a 60 DRK, I've noticed that I need to not use Unleash the same way PLD uses Flash. Yes, it's great for the initial aggro gain because i don't have to have a target, and it's centered on me. But after that, the animation for it entirely blocks out AOE markers. Most of the mobs in HW use lots and lots of AOE, and a good chunk of those use it right off the bat. If I'm focusing on that Unleash aggro, I'm going to get spanked hard and not even know what hit me. If you notice your tank going down quick and he's spamming unleash, maybe mention to him to use Abyssal Drain more.

Other than that yeah, I'd say most people are still learning their rotations and how to manage their cooldowns.