This is the guide I've used in the past.
Guide
According to the guide, it's for moving to a new server or OS. You just have to match ZCS Versions. I'm going from Redhat EL4 to Ubuntu 8.04.
Another "X-Factor" is the Samba/LDAP extension I have setup. I have the server Off-network, I've set my /etc/hosts file to point the live server host name to my test server IP so I can browse to "liveserver.domain.com" from my test server browser and have it load everything up without having to change any config files.
If you think it's the OS, there really is no good reason why I NEED to change OS, it just sounded like it wouldn't be a problem so long as I kept the versions the same. It still seems strange why all my users are gone.