Update: There seem to be some problems with login into the game which gives a Error_3 message. Blizzard has a few tweak instructions for you if these problems come to happen.
Update: Beware fake Diablo III beta invites. Don’t click on any links even if they seem to be from Blizzard or Battle.net. The BEST way to see if you have a beta invite is going to your Battle.net account page. View the image below for reference. The Diablo III beta icon will appear above your World of Warcraft or StarCraft II icons. The beta invite email was sent several hours after I had checked my Battle.net account page. That’s your safest bet.
The fiery gates leading to the Burning Hells have begun to swing open, and the Diablo III beta test is officially underway. Invitations to participate in the beta test are now being delivered to the chosen heroes. As with beta tests for other Blizzard Entertainment games, the testing process for Diablo III will occur in phases. In addition to selecting players who have opted in via their Battle.net accounts, we’ll also be providing keys through beta promotions and giveaways — stay tuned for more info. We welcome those invited to provide feedback or report bugs on the official forums.
If you have a beta license, you are free to show, share, or talk about any portion of the beta content to which you have access, as this beta test is not confidential.
We’d like to remind those looking forward to an invite to be wary of phishing attempts. If you believe you’ve received an invite to the Diablo III beta test, it’s best to refrain from clicking on any links in the email, and instead log in to your Battle.net account to see if a Diablo III beta game account was granted. Or, if you were sent a key, attempt to add it manually by going to the Add or Upgrade a Game section of the Battle.net account management page.
For those who have received an invite to the beta test, we thank you for helping us test out our server stability and hardware. For those of you still hoping for an invite, we wish you the best of luck and hope you’ll keep an eye out for some of the beta-key giveaways and promotions we’ll have right here on the Diablo III community site.
For more information, please see the beta opt-in announcement and FAQ.