well, it's a tough one... Intellectually, I agree with you, but it's sort of a gut feeling. The issue is that as a start-up you are limited in resources. So how many campaigns can we run? How many friends can we nag to use our service time and time again? etc. You don't want to exhaust your resources at the beginning. Of course we will launch and iterate, but this is just a fear. Is it rational? Maybe not. I hope not :-)