I received an invitation email saying you've granted me special access to http://bitcoin.stackexchange.com. When I log in, it says "Come back when we're open to the public." It also says:
p.s. If you committed to support this site on Area 51, you should have an invitation to this beta in your email. It’s important that you follow the link provided in your private beta invite email, because it may contain a special token granting you access. Also, you’ll need to use the same email and login credentials here that you used on Area 51 so we know who you are.
But the link in the email doesn't have any special token; it is just exactly "http://bitcoin.stackexchange.com".