There was a story on Digg that concerned hot linking and what the person done to stop people on myspace using his bandwith and image. Now usually its polite to ask if its ok to hot link to someones image or anything else they have online, because they may be paying for thier own hosting and once the traffic goes up, then they get charged.
Well this happened to him, at first it was small and didn't dent the bandwith he was paying for, so he let it go. But then the hits jumped and he was starting to look at a big bill for the bandwith used. So he changed the image that everyone was hot linking to, and waited to see what happened. Lets just say it was a very nasty pic LOL. Now would i have done the same thing when a simple block line would have stopped them? Yes because its so funny to see what people would say when they realise that the image has changed.
Yes its nasty to do, but it teaches people a lesson that its polite to ask first.