As it turns out, you haven't until you try to just get a normal Halls of Reflection run done to complete the Wrath of the Lich King quest. I was healing on my shaman, always without having any issues, nobody came even close to dying... but damn, those tanks were selfish twits.
Tank #1: confused death knight
On the third wave of mobs or so he asks if the event has been nerfed. Well, it has, but it's also considerably easier since it's only normal mode. We tell him this and he goes, "Oh, this is normal? I wanted heroic!" He graciously stays until Falric drops his epics, then he leaves the group. Since the event continues regardless, we end up wiping without a tank and the group falls apart.
I had a little bit of sympathy for this tank because I've selected the wrong difficulty on the dungeon finder before, but frankly, there's no reason he couldn't have stayed another five minutes to at least get us to a point where we wouldn't automatically wipe as soon as he left.
Tank #2: paladin loot whore
On my next run I got a paladin tank. Again everything went smoothly, until Marwyn dropped the Splintered Door of the Citadel and the tank needed on it. I barely had time to congratulate him on the upgrade when he already left the group, clearly thinking along the lines of: "I got my loot, screw you guys!" Me and two other dpsers spent about twenty minutes waiting for a new tank until I gave up and went off to do something else.
Tank #3: paladin loot whore #2, now with extra malice
On my third attempt to complete the instance, I once again ended up with a paladin tank. I looked at his shield and it was a blue. Would this one end up being as much of a jerk as the previous pally? The Splintered Door dropped again and once again I typed out a "grats" in chat. He thanked me and moved on towards the next trash mob. My heart swelled with hope as he pulled... and then he left the party, while an angry skeleton beat up the dpsers. Fuck you too, buddy.
Tank #4: paladin loot whore of a different kind
Me and a dps death knight hung around this time and waited for a new tank. This time we actually got one after ten minutes or so, so we went on and finished the dungeon. Bone Golem Scapula dropped from the captain's chest and my eyes lit up as it's an awesome weapon upgrade for my resto shammy. I hit need... but so did the tank. He won the roll and instantly quit the group afterwards.
I have no words anymore.