Being able to confirm your email without waiting for a verification email would be a major improvement to many registration processes. In theory this could be done using a technique based on OAuth, OpenID or similar. Of course, both the site and the email provider would need to support this, in a compatible way.
This leads me to wonder: Have there been any proposals to do this?
Edit OAuth has similar functionality is that email can be auto-filled. However, this does not verify the email. If OAuth provider on foo.com says a user's email is firstname.lastname@example.org then we have to either trust the provider, or reverify. However, the OAuth provider on foo.com can confirm an email address like email@example.com.