A penguin for your troubles.
As comfortable as you may be with the way you've been playing World of Warcraft for years, it's time to change something in the routine because Blizzard demands it. It's all for a good cause though!
On November 11, 2009, all current World of Warcraft players (except for those in Europe, who have until November 12) will be required to merge their World of Warcraft accounts with a Battle.net account in order to log in to the game.
Why do you have to do that? Well, Blizzard is expanding and enhancing its online services, and there's really no better way to populate the user base other than to get all the WoW players on board.
Blizzard wrote in the FAQ: "We’re getting ready to launch the new version of Battle.net, which will include a number of new communication and community features designed to enhance World of Warcraft play, such as cross-realm World of Warcraft chat, cross-game chat (with the launch of StarCraft II), real-life friends lists, and more."
Whether you like it or not, you're going to have to merge over to Battle.net--but Blizzard will be giving to you a brand-new penguin in-game pet named Oswald (perhaps in reference to the Batman villain?) as compensation.
Read more about the process and how to migrate over to Battle.net here in the FAQ.