Don't check your email. Instead, go to Battle.net and log in to your account. If you don't want to go through the Battle.net site, you can also go to the official World of Warcraft website and click on "Manage Account" to log in there. Once you're on your account page, click "Home" in the upper left of your screen to go to your home page. You'll see a section labeled "Manage My Games" there for your perusal. Do you see an icon with the Cataclysm logo? Congratulations, you're in the beta! If not, you aren't in the beta yet -- keep checking back every now and again to see if the status changes.
If you receive an email from Blizzard, no matter how convincing that email may look, don't click the links in the email. Instead log in using one of the two methods above to verify whether or not the client is there first. As scammers and keyloggers get more and more clever, it's necessary to take a few extra steps to verify what's actually going on. So did you make the beta? Are you in, or still waiting? I have a few friends that have no interest in even seeing what the beta has to offer -- they'd rather wait till release and experience everything fresh and new as a surprise. Do you fit under that category? And most importantly -- goblin or worgen?