Great idea... but the issue I am having with this any every other mail list plug is that it vendor focused. The whole reason why we send out mailings to increase sales. With this plug-in, my customers have to signup and then signup again to actually buy something. This just doesn't work for many of us because our potential customers get frustrated with the "why do I have to do this again".
I don't care what what GetReponse, iContact, etc.... says about conversion rates. If you want any of these conversion rates = 5%, make the process customer centric instead of vendor specific.
Here is what this means to plug in developers like this. We need a plug-in that is customer focused where the subscriber is added to a local wordpress database ( a basic profile is setup). The plug-in then is configurable to sync with a mail-list vendor of our choice. Newsletter requires are pushed to them while opt-outs are push backed to us. This approach is business and customer friendly by creating a seamless approach. It also allows, us the business, to easily migrate to any contact management system by just adding them and letting the system synchronize the lists.