Hi Kenny,
I've fixed this and it wil be in svn trunk by tonight.
For an immediate fix you can set the RegexValidationExpression on the Validator in ManageUsers.aspx and in Register.aspx to this:
^([0-9a-zA-Z](['-.\w]*[0-9a-zA-Z])*@(([0-9a-zA-Z])+([-\w']*[0-9a-zA-Z])*\.)+[a-zA-Z]{2,9})$
Best,
Joe