From this WOW webpage not linked anywhere but available to everyone, Blizzard seems to have called employees' "friends and family" to alpha test the incoming expansion The Burning Crusade.

On this webpage we can read:

The Burning Crusade Friends and Family Alpha Test (the “Friends and Family Alpha Test”) is a limited period during which certain designated people (“Alpha Testers”) are given the opportunity to test the pre-release version of Blizzard's “World of Warcraft: The Burning Crusade” expansion to Blizzard’s “World of Warcraft” massively multiplayer on-line role playing game.

And very interesting is the eighth point of the agreement:

8. Confidentiality. The existence of the Friends and Family Alpha Test and all elements thereof (including without limitation this Agreement) is confidential, and you agreement to maintain secrecy associated with the Friends and Family Alpha Test until such time that Blizzard releases such information publicly. For purposes of example and not limitation, you agree that you will not disclose the following:

(i) The existence of a Friends and Family Alpha Test.

(ii) Your role as an Alpha Tester.

(iii) Any details regarding the stability of the Program, including, but not limited to connectivity, server stability, frame rates, lag, etc.

(iv) Any comments regarding the appearance, look, feel and playability of the Program.

and so on.