Normally I post a patch but I do not have a lot of time right now and this change is simple.
To get the 6.x-dev version working change $form['form_id'] on line 17 of civicrm_theme.module to $form['form_id']['#value']
With that change, everything seems to be working fine for me.

The attached patch adds a third theme selection for civicrm pages which the user defines as 'public.'
This allows, for example, CiviEvent pages to display in the default theme, but still use an alternate theme for managing contacts.

We needed to have an "internal" theme and a public facing "external" theme for all public pages, whether logged in or not. While civicrm_theme helped us theme our "internal" pages similarly to admin_theme, certain elements of CiviCRM our public facing and needed to be able to be defined with a different theme than that of the rest of CiviCRM.

Tiny patch to handle this.

This is a hook_uninstall patch that should get rid of any traces of civicrm_countblock should it be uninstalled.
List of Destruction:

• Variables
  • civicrm_theme
  • civicrm_admin_theme

The theme switcher is working great for the pages have have "admin" in the URL. However, there seems to be quite a few pages that are really admin pages but fall under the User theme such as the Dashboard. It would be great if these pages could be controlled by the admin theme as well.