If you have proof that someone else is using your account illegally, then fine. But you can't just say "it wasn't me" when your account shows a ton of illegal activity. Granted, no one can prove you actually did it. But I think the circumstantial evidence provided by the account activity is good enough to convince any jury.
True, if they have evidence of 1000 downloaded files over a period of 3 years, then yea, you're probably screwed. But to say that if another person comes into your house and downloads a file off your network and it's your fault is stupid.
The litigation itself might bankrupt you, but it's stupid and costly for them to do it to every schmoe who took one movie off the net. They also kill their customers.
All I can say is thank God the Australian authorities don't have the power to go after people yet We had the MPAA send numerous letters to the ISP in which I use, The isp threw them out and didn't even notify the customer