Another advantage of "first come, first served" for a limited number of customers: you can performance test your app and use the data to determine the N you allow to signup. Your slow site doesn't piss off your early adopters AND you delay performance tuning until you want to go to a larger audience.
You also make your own exclusivity. In fact, you should stipulate that during the early access period, idle accounts will be reclaimed. That'll get them to come back (if they're at all interested in your service).
You also make your own exclusivity. In fact, you should stipulate that during the early access period, idle accounts will be reclaimed. That'll get them to come back (if they're at all interested in your service).