I've heard about a few examples of this happening lately, and the circumstances seem kind of sucky for the following reasons :
1) As stated before, you need to have a really good reason for your character to kill someone. Subdual isn't there to add flavor, it should really be your default method when it comes to any PvP (if in doubt, subdual! Nobody minds losing a few items, but an entire character is another matter entirely)
2) Nobody can 'walk in' on you killing your prey, or sacrificing them to whichever dark god takes your preference while you smear yourself in blood. This seems like outright metagaming to me. There's nothing 'safer' than killing someone in a QA. Nobody can stumble on to the body or whatever. So unless you have a reason within the quest itself (the halfling fireballs you, killing all your friends) then it's best not to do it.
3) It's not much fun for the other player, particularly if during a difficult battle, for no reason, you get killed or left to be killed by the others in your group, and then get told you're being fully-looted.
I appreciate that EfU is a full-PvP server, and have always stated my opinion that done correctly, it can enrich the server greatly to have. I just think it requires some fairness, common sense, and simple courtesy to make it work properly. Sometimes, there's a very thin line between fun-PvP and griefing somebody.
Remember, ALWAYS try to get a DM's say-so beforehand -if possible- (though that's not to say that you need a DM to oversee every player conflict you're ever involved in), and if you can't, then use common sense to determine whether you have a good enough reason, or if in doubt, simply use subdual. Being afraid of retribution OOCly isn't reason enough to not leave someone alive ICly, if you follow that logic.
Cheers.
NC