Hi - I'm using WP 3.4.2 and Newsletter 3.0.9 on my site at http://www.TrustworthyCare.com
I've created a blank page at http://www.trustworthycare.com/email-newsletter/ to use as the "Alternative custom confirmation required page" and I've entered that URL in the appropriate field for the "Alternative custom confirmation required page" in the Confirmation tab in the Subscription settings page for Newsletter.
However, that setting appears to be ignored and the confirmation box still appears instead of the page that I created. That's not what I want, and also it is a security hole because the URL for the default confirmation box allows the user to browse the plugins files on the site (!)
Please give it a try on my site, and let me know if you can see something that I'm doing incorrectly.