What kind of bandwidth do you burn and at what cost. I know they burn a lot. I wonder if it's worth it.

well, it's a bit different type of hosting and it depends from the sites /customers you host. there are some that will burn 20gb/month and some require 1TB/month easily.... hard to predict...

ps. also problems with illegal content/images/tgp etcetc...

Watch your toes, but if you're careful enough it can be extremely lucrative.

A lot of porn sites crank out well over 5TB/mo.

The biggest danger with such high bandwidth clients is that dealing with the loss of business if they go under or get shut down. You can end up in a situation where you have two large porn clients pumping out 140mbps combined, and the rest of your business eats up only 15mbps. Lose one of those clients, and you might end up with a 100mbit circuit you don't have a use for.

As for the abuse aspect, if your network is setup right it shouldn't be much more of a problem than any other client.

Controlling their bandwidth can be a bit tough. Make sure they all use a password protection service too (my company developed Killersecurity for the prime purpose of curbing some of our client's bandwidth spikes due to password leaks and brute force attempts)..