This is a great hack! I was wondering if it could be taken "one step further" though, for instance- in addition to checking the username for duplicates, how about turning this new feature on or off for any other user profile field(s) which would be flagged via a checkbox within AdminCP>UserProfileFieldManager>EditUserProfileFie ld ?
This would be useful for admins who would have the need to prevent duplicate users based upon custom profile fields such as (for example...) "telephone number", "social security number", or any other custom profile field for which Administrators want to use as an identifier to prevent duplicate registrations.
(please)