Meh, I just keep aoe threat on everything and let the dps do whatever they want(probably a side effect of leveling monk and blm first and being annoyed when tanks would lose hate to spread dots). Except for the few enemies that absolutely need to be burned down quick(like qarn bees or vigils dragons) I've never seen much point in focusing down one enemy at a time. More tanks need to start taking loss of aggro on a mob as an insult to your ability rather than blame it on others.