One great way to create continues buzz around your startup is to release private beta invites in multiple phases. Startups often choose to do this at big events in collaboration with media partners to generate publicity and attract new users. The feeling of exclusivity of the participants will motivate influentials to sign up and hopefully write about your company. A good example of this has been the madness surrounding the Google Wave invites.

There are a few problems which startups seem to face in the process of rolling out invitations. In the case of Google Wave many people with an invite discovered they had non of their friends on the service to interact with. This is not beneficial for the user experience of your new service. Another problem is