Earlier this month, a District Court in California ruled against a copyright holder who had wished to obtain the identity of a number of BitTorrent users by subpoenaing the ISP identified with the piracy. The copyright holder, Hard Drive Productions, wanted the IP addresses of the users who participated in the illegal file-sharing but didn't wish to pursue the matter in court. Wisely, the District Court judge sense that Hard Drive essentially wanted the court to do the dirty work for them but not actually employ the court system to prosecute the accused copyright violators and therefore ruled that the ISPs didn't have to reveal the identity of the alleged copyright violators.
Across the Atlantic, a similar case in which copyright holders have demanded the identity of an alleged pirate be forfeited by a Swedish ISP wherein the European Court of Justice has decided that, yes, the ISP could be required to hand over the IP "which was allegedly used in an infringement." This doesn't mean that the ISP must now hand it over, per se, but rather that the case will return to Sweden's Supreme Court in order to determine if the IP address will indeed have to be shared with the copyright holders.
While this case is a suit to obtain the identity of one person who stored 2,000 audio books on his server whereas the California case was about ninety BitTorrent users, the same concerns cited by Judge Howard R. Lloyd in the BitTorrent case still persist, namely that the process of identifying the user via IP address is no guarantee of identifying the culpable person.
Since the EU case is focused on only one user, it creates a dilemma between how courts should arbitrate when an ISP handing over IP addresses associated with illegal file-sharing. If it's one, the thinking seems to be that the risk of misidentifying the copyright infringer is low; but if multiple identities are being requested, however, the risk of misidentifying copyright infringers goes up.
Granted, these courts from country to country aren't expected to rule in accordance.