Hey Jamie,
Kind of a bug turned up when fixing John's "moved behind a firewall" issue. I set the "Default IP address for DNS records" to his outside IP, and then used the Change IP Addresses page to reset all of his hosts to VirtualHost on 10.0.0.1. That part worked fine...but the DNS also got altered to the internal address, where we wanted it to stay with the outside IP.
I can imagine situations where both would be the desired behavior (and it could be unintuitive to hit "Change IP Addresses" and not have it change the DNS just because the default is another IP), but I don't see any way to do what we needed in this case. Since it's such a common task, and I've written up docs for the switch in the new admin guide, it'd be good to have it an accessible action. Maybe a button on the change IP form that just says "Use IP for DNS records" with options "Use default IP from module config", "New IP", "IP address _____". And of course we'll want a help file to explain the difference. I can foresee this being a bit confusing...