Since I just got one of these scam e-mails, I thought it would be worth it to mention that another wave of beta invites is indeed going out soon from Blizzard (if it hasn’t already). But, as a precaution, DO NOT CLICK ON ANY LINKS IN THOSE E-MAILS. This time around, it isn’t a code you enter to get access to the Cataclysm beta, your Battle.net account will simply be flagged for beta access.
If you get an e-mail saying you’ve been invited to the Cataclysm beta, go the the Battle.net account management site, log in using your Battle.net e-mail, password and optional six-digit authenticator code. You will then be taken to your main account page, which will list all the Battle.net supported games that you have. Your standard installation of World of Warcraft will be in there (likely with the Wrath of the Lich King box art), as well as any other Blizzard titles (StarCraft, Diablo II, etc.).
If your account is truly flagged for Cataclysm beta access, you will see some box art for the expansion there, as well. Click on “Manage Game” underneath it and you’re good to go.
I repeat: DO NOT CLICK ON ANY LINKS IN A CATACLYSM INVITATION E-MAIL. There may indeed be a legitimate link Blizzard has placed in the e-mail to the Battle.net log in site, but why risk it? Just go there yourself, log in and check.