We do IP bans. What happens after that is really up the person. There have been cases where we had to ask the ISP of the user to intervene.
We also, proactively block proxy services.
That is not to say people do not creep back in. If they do and they can manage to respect the forums, we do not care. If they act out again, then we go through the process, again. Some people never get it, some do. I always have to giggle a bit when someone thinks they sneak back in and are getting away with something.
While I would rather be doing other things, this is something we have to deal with.