Using Characters in Usernames in WPMU

Hello!

I am trying to allow users to use their email addresses as their usernames for my wpmu site and was having a bit of difficulty setting this up. I found this previous thread but was unable to allow for an email address to be accepted within my framework, any ideas as to what could be causing the editing out of the sanitize_user() function to not work? I followed the steps outlined in the post below as well as a few different markups...wasnt sure if any new features in wp or using wpmu might affect this mod a bit differently. Thanks a ton for your help!

http://wordpress.org/support/topic/special-characters-in-usernames

Also, was thinking about this last night...If this change were made is anyone aware of any security issues this may pose? Just thinking that there could be an underlying reason for the disallowing of symbols that i might not be aware of.

Thanks again!

Erik