Setup an IP ban?

First of all, I'm sorry for my english that isn't perfect, but whatever...

Today, I though about a new ban system when i miss click and block a friend, but when I want to unblock him... I realize I just can't see the end of my black list, and I'm pretty sure some of these account was created and played by the same player. And it was fully normal, that's a react everybody have... "I'm ban? Well, go on another account"

So, I though that an IP ban could be more interesting. By the way, i know this system got his problem too, some of FAI deliver dynamic IP and it's pretty easy to change it oneself if the IP doesn't change automatically.