AWeber has introduced Facebook registration for AWeber email opt-in web forms.
When AWeber users enable Facebook registration for their web forms, visitors will automatically have their name and email address displayed in your form if they are logged in to Facebook.
Those not logged in to Facebook will simply see the normal web form.
The Facebook feature is easy to use on new and existing forms in AWeber. There is a checkbox during the web form creation/edit process.
Then, when you place the form on your site or send people to the AWeber hosted version, the Facebook registration will be available.
I would suggest incorporating this into your list building strategies right now, because it makes it easier for people to opt-in, emails collected this way are more likely to be valid, and there is no chance for typos.