I am grateful to vnunet.com for referring me to Priority Records and others v Chan. Vnunet reports the case with a hint of glee as an unmitigated defeat for the recording companies. Having read Judge Zatkoff's judgment I am not sure that that was actually the case.
It appears that the claimant copyright owners sued the wrong defendant. The IP address of the computer that had downloaded the allegedly infringing files belonged not to the defendant but to her 13 year old daughter. The claimant then applied to join the 13 year old with the intention of adding the mother to that claim as a joint tortfeasor on the ground that she had given her daughter the computer. As the case as first pleaded was obviously unsustainable the claimants applied to discontinue their original claim while reserving the right to join the mother as a defendant.
The question before the judge - the case was in the US District Court for Eastern District of Michigan which is roughly equivalent to the Chancery Division in England and Wales - was whether the case should be dismissed altogether or whether the claimants should be allowed to discontinue the action and bring a second action later. They invited the mother to consent to those terms but she refused to do so seeking by cross-application costs against the claimants.
The defendant did not escape entirely criticsm by the judge. He noted that she had refused to consent to an order that would have saved costs, that the claimants had tried to join only those responsible for the infringement, and such costs as the defendant had incurred resulted from efforts to hamper the efficient prosecution of the claim. Accordingly, he granted the claimants' application to discontinue and refused the defendant's application for costs.
Vnunet states that some defendants to file sharing suits have counterclaimed with antitrust and racketeering. It is not clear how whether any of those counterclaims has succeeded. In Europe, abuse of an intellectual property right can occasionally infringe art 82 EEC as in Magill, Radio Telefis Eireann and others v Commission  EUECJ C-241/91P (6 April 1995) but these cases are rare. Having said that, some of the file sharing claims on both sides of the Atlantic have occasionally seemed a little heavy handed.