Blizzard posted the following yesterday regarding signups to the open beta servers.

World of Warcraft Open Beta Signups Closed
The overwhelming demand for the World of Warcraft open beta test has resulted in hundreds of thousands of successful signups. We have already reached our target number of testers and therefore must regrettably close our account creation pages. We'd like to thank everyone for showing such interest in joining the World of Warcraft open beta test and would like to reiterate our appreciation of your continued patience during our website outage. Please note that we will continue to analyze server population, and should there be more space for testers prior to the game's launch on November 23, we will re-open the signup pages.