We should have a plan for public beta start, like
- publish on the mailinglist?
- News article on joomla.org?
- post on the forum?
- get extension developers to mail there customers or write a news?
- extend docs.joomla.org with the new Q&A site?
- motivate Joomla magazines to promote the site?
The FAQ in the mail makes it clear:
Q: How can I help the site succeed?
A: The minute the public beta opens, invite your friends. Spread the word via Twitter, blogs, and email far and wide. Hang out on the site answering incoming questions during the first few hours so that newcomers understand what a great experience a working, popular Stack Exchange site can be.
so we should be prepared for that day!