I think it depends a lot on what your service is. I'm working on a startup for hikers (trailbehind.com) and we were live from day one. But most of our traffic comes from searches, and we've gotten more and more traffic from searches as we've gotten better and more popular. We've also had some hard core outdoors fans find us and send us great suggestions and even data. But if we were a service like Pandora, that model wouldn't have worked, since people would have had to remember to come back after a bad experience.