I can't raid at the moment because I can't guarantee that I can be online at any particular time, and when I can get online I have to stop playing every five minutes to change nappies, comfort crying child etc. I've been grinding heroics with my tank and my arcane mage alt instead.
Although heroics are easy these days now we massively overgear them, there are still some places where even a well geared tank can still die if you are not careful. Here's a list of four which occur to me. I've ignored the three new instances because they are definitely not AoE fests. I've also ignored places which impose any difficulty of execution (eg Skadi's gauntlet in UP) - I am only interested in mobs with surprising and dangerous abilities.
Utgarde Keep - The very first room has mobs that sunder armour, which debuff stacks to five. It's tempting to charge in and pull the whole room, but if you have a full whack of sunders up then the mobs can melee you for 5k. If you have four or five mobs beating on you for 5k per swing then even a well geared tank can die very quickly.
Old Kingdom - The Ahn'kahar Spell Flingers have a spell which does damage equal to 80% of the target's maximum health. These guys are also found near the start of the instance before the first boss. The spell can be reflected (woo hoo 50k hits) or interrupted, but again leaving these guys up too long, or pulling two packs (there is one per pack) can often lead to a dead tank.
Azjol Nerub - The Anubar Prime Guards have abilities to reduce the damage they take, increase the damage they do, and cause AoE damage whenever party members are healed. These should not be a problem if dps is awake, but what often happens these days is that the tank will rush ahead of dps and pull the mobs, meaning that the debuffs on the tank stack up several times before dps starts. By the end of the fight the mobs will be hitting quite hard indeed, so you may need a cooldown to survive depending on your gear level and how strong your party is.
Gundrak - The elementals before the Drakkari Colossus drop a mojo puddle which does 1.6k dps on heroic. This should not be too much of a problem, but again since it is normal practice these days to pull the whole room you can have overlapping pools and damage can stack up quickly if you are not aware or if your healer is not up to it.