Most script-kiddie trolls are usually on AOL or some other "parental control friendly" ISP that dishes out dynamic IP addresses. I've been stung by bans based on IP addresses when the purpetrator used a dynamic address.
Dynamic IP isn't the problem, you can ban a whole subnet if you want. Problem is proxies, I have been banned from a site and just used a proxy to get around it. So many public http proxies around.