The beta is only open for US Citizens, and they will probably have to sign a NDA to do it too. If they leak any information, chances are that they will be sued into Oblivion.
Yea , there is a NDA...
Believe me, you would have to be more insane than sheogorath to come on the forums and post a spoiler after signing it. I have done beta's before, they wont play around if you breach a legally binding contract with them.
(of course someone will, but that will be the last thing you ever hear from them)