404's paid for our company's very first server back in 97 or so. It was an old hosting company server, and all the IPs were getting traffic from where the client's sites used to be.
We learned early.
100free.com was the first host to get banned from the Hun for selling 404's. If you've ever had a freehost, you'll understand that you can come up with a lot of 404's at times. And there are a lot of things you can do with 40,000 404 hits a day.