How do I migrate my GetResponse subscribers to 1ShoppingCart?

Is there any reason why migrating my newsletter subscribers from GetResponse to 1Shoppingcart would be a bad idea? Additionally, is seven weeks of one weekly reminder long enough to encourage most of my subscribers to make the transition? I am offering a free ebook download as an incentive to those who do switch. Are there any tips or resources to help me enact this transition with minimal disruption and annoyance to my subscribers?