So i had the request in building my wpmu site was for the ability for users who have already created a login name on what will be an external html based site to be able to use this same login information on my wpmu site. I thought that giving wp access to the outside database might be a bit complicated while still allowing users who are not registered through this outside site to simply register on the wpmu site. The thought here was since the sites are going to be closely related it would be nice for people to have the same username/pw combo for easier remembering.
My thought though was, has anyone had any experience with the WP Email Login Plugin with Wordpress MU? Or for that case, im actually unsure why wp limits you to not using characters in the username. Is there a way that this could simply be modified perhaps? Thought that there was probably a rational reason wp excludes characters but wasnt sure. Just kinda curious!
cam across this as well, appears people have talked about it but nothing has been established - http://wordpress.org/support/topic/allowing-registration-with-the-email-as-username
Thanks a lot for your help and look forward to hearing your thoughts on the best way to allow users to use email addresses as usernames!!!