User not completing registration

[The Finman]

I'm not sure if I understand your question completely.

If you are talking about anyone that clicks on register but doesn't fill anything out, then no...nothing that I am aware of.

If you are talking about someone that fills out their registration but never validates their registration by E-mail, simply go to Usergroups in your AdminCP (in either 3.5.4 -3.6.0 (don't know about earlier versions), and as long as you haven't changed your default usergroup settings, there should be a usergroup called Users Awaiting Email Confirmation, that will have all the people that registered, but never verified their registrations...if that helps.