Same if you block him after x IPs. Banning does prevent new users from signing up from the same IP (if you have that setting enabled). I'd also enable StopForumSpam blacklist checking and submitting so all his usernames, emails and IPS are submitted to the StopForumSpam database each time you ban him. This will make it increasingly harder for him to keep signing up (along with enabling email verification since he'll have to create a new valid email address each time).
