George, depending on the user we have a few options.
1) Ban the username.
Con: The user can simply re-register.
2) Ban his IP range.
Con: A few other members in the trolls area may be banned as well. This wont work with dial up users or users with dynamic IPs.
3) Set global ignore. Nobody sees any of the trolls posts.
Con: If the troll logs out, or has a 2nd username, he can see that his posts dont show up.
4) Cant go into much detail, but this setting will show random errors to the troll. It looks like the site is having problems. Only one out of 50 page requests show up correct. User can not logout, post, reply, or do much on the forums. VERY FUN TO USE!
Cons - None!
There are a few other things we can do, but rarely does it get to that point. We rarely have mroe then one troll a week hit the site. Chances are, you never relize they were on the forums. We have some good mods to clean up that stuff.