These pesky bittorrent lawsuits continue to propagate themselves throughout the court system. Content owners -- which frankly may have a legitimate beef with having their films distributed for free -- persist in using them as tools to issue subpoenas seeking the identity of alleged file sharers. If you receive a notice from your ISP that it has received a subpoena and that your personal information will be disclosed to the plaintiff unless you take steps to stop that from happening, don't despair.
One of the first things you should do is check the status of the lawsuit. Many of these cases are getting dismissed by judges who are increasingly skeptical of both the methods used by the plaintiffs, and the quality of the rights they claim to hold. If your case has recently been dismissed, then you may have a great argument that the subpoena is no longer valid. Even the most compliant of ISPs will be nervous about disclosing customer information in response to a subpoena that has no legal force.
Those of us who handle these cases can quickly let you know what the status of the underlying lawsuit is. Make sure you double check that before deciding how to respond to the ISP notice.