The ability to add additional fields to the registration form is really useful. But for some people all the additional info is a turn off and the bail out
Would it be possible to make it two stage registration?
The first stage is the basic WP data. Email address, (possibly first name and last names). Quick and easy KISS. BOOM!
The next stage, where the additional fields have been added, occurs on “registration2” page after email confirmation where the visitor is referred to the “Complete Registration Page” and now where the additional fields are required to complete registration.
At the very least the email address has been given. It could be possible to integrate with an auto responder to encourage the visitor to complete registration if they should bail out on seeing the second page. This could also be part of the AR sequence to move them from #00 level… “Failed to complete registration”… ( no not that 00 number 
Anyway, it is just a suggestion – It is getting harder and harder to get people to sign up and keeping it as quick and simple as possible … to capture their email is preferable to trying to grab all the visitor info in one hit.