The Elder Scrolls Online have just announced that they have sent out the first "small wave of invites" via email, for public beta testing. Judging by the amount of disgruntled posters on their Facebook page it definitely does seem like a small wave indeed. But keep your hopes up, they have stated that email-less folk should "not be discouraged" as they will be sending more invites soon.
So if you have signed up but not received the elusive invite email then don't despair, and keep checking (especially that damn spam folder)! And if you haven't checked yet then why are you still reading?? GO!! GO CHECK YOUR EMAIL NOW!!
If you have yet to sign up, and want to, you can do so at http://signup.elderscrollsonline.com/