They'd first sold out back in March. Then, like sweet, sweet relief, Blizzard announced that more tickets were available yesterday. Now, less than 24 hours after the additional tickets were made available, the Blizzard Entertainment Worldwide Invitational is sold out again. Of course, the news blurb on the official site encourages you to keep checking back, so it's possible they'll announce more ticket availability yet again. There had been some payment problems, so maybe this round of new tickets were a concession to that issue.
For those just tuning in, the WWI looks like it's going to be quite the hopping place. There's an Arena tournament scheduled, and L70ETC is going to be rocking out. You'll probably be able to spot a mailbox performance by a few Night Elves in their dance tournament. Don't forget to hit the fan art contest and machinima contest.
Keep an eye on WoW Insider -- we'll let you know if tickets somehow become available again.