We have a few other things we might try to keep the sockpuppeting to a minimum. I'm not going to discuss our strategy here.
To answer the OP, banning an IP address is a bad idea, especially with cable modem systems which rotate out IP addresses on DHCP leases. Imagine how mad you'd be if your next door neighbor got banned, then you ended up with his IP address a week later.
Or if you played at school (ahem, after class), and realized some forum troll for the school's IP address perma-banned.