The public beta was supposed to start a few minutes ago, but the login page still says the site is in private beta for another day.
2 Answers
It's public now; the Area 51 e-mail went out and you can get to the homepage without logging in
Update: It's now public, of course.
I see I'm not the only one trying to catch the moment. :)
The Area 51 page says that the public beta is about to begin shortly.