Jack-o-Lantern wrote me, because he was wondering whether the Blizzard authenticator had hidden implications. Using it certainly increases the security of your account. But it also makes it harder to sell an account, because you would need to send the authenticator by normal mail, not just UserID and password by e-mail. And it makes it harder to share accounts between guild mates, or give your account temporarily to a powerlevel service. Thus the authenticator cuts down on a lot of behavior which Blizzard previously had problems stopping.
Right now Blizzard can't produce as many of the authenticators as people are willing to buy. But I'm guessing guilds in which a lot of account sharing is going on simply won't buy the thing. So what if later Blizzard makes the use of the authenticator obligatory, for example by packing one in the next expansion box and only unlocking accounts for the latest expansion if it is protected with an authenticator?