A lot of sites create "buzz" with an invite-only period. That got me wondering if there's a way you could limit enrollments to groups of people -- maybe a mini

A lot of sites create "buzz" with an invite-only period. That got me wondering if there's a way you could limit enrollments to groups of people -- maybe a minimum of four? -- and have them all choose a common start time for when their accounts will first go live. Then send out the invitations at the same time, so they all log on at the same time, so there's conversations and interaction for everybody from the get-go...