You should put the "sign up to know more" box the moment you have your domain hosted. WP Themes like http://themeshaper.com/wordpress-domain-parking-theme/ htt

You should put the "sign up to know more" box the moment you have your domain hosted. WP Themes like http://themeshaper.com/wordpress-domain-parking-theme/ http://themeshaper.com/wordpress-domain-parking-theme/ are your friend... takes 20 minutes to set this up. Add to the list of emails u get from this page the email address of everyone you network with about the idea/startup. That's kinda cheaky but it's done a lot. When u launch go through the list to spot any pr, media or VIP people -- offer them a beta. Then just launch and email blast everyone with the information.