A goal of many new Web "2.0" ventures is to build a large or at least persistent community. Success is difficult to measure, but breaking into the top 100,000 sites by traffic measured by Alexa is one goal. It might be a good sign if the site designers send emails to a few people asking them to take a look at the site and after only two days over 3000 people sign up to beta test. You could do worse than to have a list of 60,000 people desperate to join your site before it leaves beta - so desperate that the site admins put a "waiting list checker" page up just so that an impatient person can see how many people are in line to get accounts before he or she does.