I'm unable to navigate to the main Proof Assistants site. I was clicking on an item in my reputation changes notifications, and it brought up a page announcing the beta would become public "in a few days". Various other things, such as trying to post a question on the main site, clicking my avatar, or choosing Proof Assistants from the drop list at upper right, produced basically the same result.
Perhaps this is an, expected behavior at the end of private beta?
Update: This seems to have been on a PC where I'd not yet "entered the private beta". Once I'd clicked the button at the bottom of the page I could access Proof Assistants as on my other PC's. Oddly it allowed me to post to the meta site (this post) but not to see the main site.