Few people will give away their contact information unless they are persuaded by an incentive they value more than their privacy. For instance, you would have no trouble building your email list if the incentive to fill-out the registration form was an all expenses paid trip to Geneva Switzerland to have lunch with your celebrity ambassador Angelina Jolie. On the other hand, you would get significantly fewer sign-ups if the incentive to fill-out the registration form was an entry into a sweepstakes for a 1 in 50,000 chance to meet Angelina Jolie. Your subscription rate will rise and fall with the perceived value of the incentive offered to your audience.
However, not all subscribers are equally valuable to you. If your cause is saving bottlenose dolphins from extinction, you will attract more valuable subscribers by offering a bottlenose dolphin screensaver as the related incentive than you would if you offered unrelated, free movie passes.
