IncGamers has word that Blizzard Worldwide Invitational attendees have received their promised invitation to beta test an upcoming Blizzard game, but that contrary to assumptions, this does not guarantee entrance into the beta test for World of Warcraft: Wrath of the Lich King (thanks Ant). They quote French community manager "Thyvene" as saying:

Attendees of the Worldwide Invitational 2008 have received a Beta code to participate in a future phase of Beta testing for Blizzard. Unfortunately, we can not guarantee that the code gives you access to the Beta for Wrath of the Lich King in particular. Therefore, to increase your chances of being selected to participate in the WOTLK's Beta test, we advise you enter the draw held for this phase of Beta testing, via the account management: http://www.wow-europe.com/account/