With all of the early copies of Wrath of the Lich King going around, people jumping in with early installations are finding some interesting things. Reader Emil J. wrote in to tell us about a message WoW-Europe displayed when they looked at the account upgrade page.
It states that in the future, Blizzard intends to switch over from World of Warcraft accounts to a centralized account system for Battle.net. Which means that you'll create one account and you'll be able to use it for all of Blizzard's games with online capabilities in the future such as Diablo III and Starcraft II.
The hook is that you cannot upgrade your Burning Crusade account to a Wrath of the Lich King account without accepting the fact that you may be required to open a Battle.net account at some point in the future. You can still play WoW, but you can't upgrade your account for Wrath.