This is not the first time the two have worked together. Last fall Dell and Blizzard gave away five $3200 XPS M1710 Limited Edition notebooks. That was just for logging into the game and was promoted by Blizzard. This new pairing is being promoted by Dell, so they may have something different in mind this time.
Either way, you can sign up on the teaser page to be notified by e-mail when they are ready to send out their big announcement. There are also 6 beautiful pieces of World of Warcraft desktop backgrounds to download in various sizes.