(1) Your "launch" should be introducing your premium version. In other words, the day you deploy your billing code should be the same day you leave beta.
(2) Let everyone use the site for free in beta. What you lose in concrete revenue you make up for in free bug reports, feature ideas, and feedback.
(3) Tell the free users the beta is ending and they'll soon have to pay. Feel free to give free accounts to some of the prolific community members, but don't feel bad charging people for your service. It's worth charging for - that's why you built it, right?
(2) Let everyone use the site for free in beta. What you lose in concrete revenue you make up for in free bug reports, feature ideas, and feedback.
(3) Tell the free users the beta is ending and they'll soon have to pay. Feel free to give free accounts to some of the prolific community members, but don't feel bad charging people for your service. It's worth charging for - that's why you built it, right?