Wrath of the Lich King beta, you'll recall that you had to link your current World of Warcraft account to a Blizzard shop account before you could get into the game. While that was interesting, it obviously never made it's way into the game...
...or did it?
Blizzard has finally released their account merge, only you're not longer merging your account with your Blizzard shop account anymore. You're merging your World of Warcraft account into Battle.net, allowing you to use one login for all of Blizzard's current and future titles.
As a side benefit to all of this, the new Battle.net allows you to link any of your Blizzard games to your account, including World of Warcraft, and be able to download the game from anywhere, much like Steam. Since this is the case, and since Blizzard has been offering downloadable upgrades for World of Warcraft, will we be seeing the rise of a Blizzard version of Steam via Battle.net?
All future titles will be utilizing Battle.net, so it only makes sense to log in now and get your logins all converted over. All you need to do is sign up on the main page, and the website walks you through the rest.