Thanks for this great module, it is very handy.
Just some comments regarding accessibility, i dont know if this should be filed here or in the ctools issue queue. To make this module more usable to keyboard users and screen readers there are some things that should be done.
Read the article by Josh Habdas on regarding lighbox accessibility http://www.habdas.org/2009/03/29/building-a-better-lightbox/

Currently it does not shift focus to the modal, also all the links on the page behind the modal remains active. The modal is injected at the end of the page so all links on the site will be tabbed through before the user gets into the modal login/registration form.