It seems that on my installation, the banned email domain list simply not work. User with such email domain keep register and splog the community.
I've seen this normally have been fixed, and I checked my code, it seems to be up to date, but the wp-signup page don't display the "use another email domain" message.
You can have a try here : http://inda-blog.com/ wp-signup.php with one of theese domain (which are my actual banned domains list) :
@zhopa.biz
@s2worldsports.net
@d2pills.org
@d2treatment.org
@gmail.com
@a2bmw.org
@c2voyage.org
@s2sportblog.org
@rebelmail.info
@luvgolfing.com
@moviefan.com
@wild4music.com
@games.com
@allsportsrock.com
Thanks !