Hiya...
I guess this might be a feature for a premium version. We already run a website and email forums with several thousand registered users. Your system looks like it'd work well for us, but we'd need to use our existing member database without having to re-register everyone.
A feature that would allow us to use OpenID authentication or let your system call our authentication tool for existing users would be ace.
Thanks in advance and good luck with the system.
Toodle Pip
Sam