Along with my postcard mailing last month, I also participated in an email campaign to direct a specific group of people to a survey for BestPlaces. As with WifiPDX, replying to the request was actually to the benefit of the recipient.
It shouldn’t be surprising that we received a lot more replies right after each message. It seems to be human nature to either respond immediately or decide it’s not worth responding “late.”
Seth Godin noticed it in June with his eBook experiment and any salesman knows how important it is to cause action and not let a potential sale “think about it.”