Just been wondering this for quite some time now. Just have a couple of questions, really.
Say that a healer overheals mid-fight. Does enmity, as a value on the tank, get decreased when the healer overheals? Or is the healer just catching up in aggro when he/she overheals? Buddy of mine was wondering this in ST, when he wasn't able to keep aggro against a tank in the same gear as him, blaming Regen and Medica 2 for him being unable to maintain aggro, as it was supposedly the only variable different.
(...which just doesn't seem right to me, lol.)