Hey there!
Thanks for posting. Our plugin has some built-in functionality that pre-fill your input fields with the “Default Merge Tag Values” that are set in your MailChimp account. However, it’s worth noting that because default merge tag values can’t be set for the email address field, that this wouldn’t allow you to pre-fill your email address field (though it would for other fields in your list).
Our plugin doesn’t provide that functionality as-is, but it can be done by changing a bit of the plugin code. Some of the forum’s other users discuss the techniques involved with that implementation process here:
http://wordpress.org/support/topic/plugin-mailchimp-list-subscribe-form-request-add-placeholder-text-for-mailchimp-widget?replies=21
If you find that anything gets borked in the process of making these changes to the plugin code, you can always reinstall the plugin and everything should revert back to its original state!
