Steel,
I just tested this method of positioning, and it works like a charm for OPC and the admin side. In the address book (when accessed from my account tab not OPC) it does not automatically re-position the fields, because they are hard coded into the template.
An easy fix though, moving the fields in the templates are easy as pie. To edit the address book fields you can look at /common_files/customer/main/address_fields.tpl
You can see it working at my test site:
http://trainingpen.com
Moving the fields in the address book or in FLC has never been a problem. It is OPC where this change is difficult, and requires some custom code like I suggested above. If you are using FLC then you just change the language variable for fax, and reorder the fields in the template. No need for any hair pulling.
In OPC the fields are populated in the order that they are pulled from the DB.