On the plus side, you can change the battle.net e-mail address, which is a luxury you don't have with the old userid, so if you signed up with an address that you've used elsewhere, find spam in a new one or have another reason to believe it may be compromised, you can just get a new address and change over.

But still, it's an e-mail address and I dread the weeks following the full changeover. It's going to be back to 10 spam whispers a minute from compromised accounts.