Yes, it's big. It's nasty. And it'll one-shot folk.
A thread on the US shaman forums discusses the "Reckoning bomb".
Haven't experienced this in battlegrounds, and it requires a particularly sadomasochistic holy tincan, of course, but still.
Basically Reckoning is a talent paladins can choose to get an "extra attack" (ala thrash, ironfoe, hand of justice or windfury) whenever they are critted.
The attacks will unleash when they try to do a melee attack.
Basically you can stay out of autoattack, soak up the damage, do your usual healing and then, after sucking up a crit or 10 autoattack your victim and unleash 1+10 attacks. At once.
Paladin dps sucks. A lot. Riiight.
