I would like (recurring and previously registered) visitors to be able to login at the end of the form so the entered form data gets stored under this existing user.
If the user is new, he can just register using the register add on. If the user is logged in already, none of these fields show.
Please see this topic for reference:
http://www.gravityhelp.com/forums/topic/user-login-at-the-end-of-a-form#post-184038