You might recall a court case, al-Haramain v. Bush, that was filed back in 2006. The case alleged that the US government had used warrantless wiretapping against the Islamic charity foundation, in contravention of FISA. The plaintiffs had based their case on a set of classified documents, allegedly logs of wiretapped phone conversations, which the government had accidentally sent to them during an investigation of the group. The government then confiscated the documents and said that, as the documents were classified, they could not be brought into court as evidence of wiretapping. Back in July 2008, Ninth Circuit Judge Vaughn Walker agreed, stating that the plaintiffs would have to produce non-classified evidence of wiretapping in order for the case to proceed.
Fast forward to January 2009 - Judge Walker has ruled that the plaintiffs have presented sufficient evidence for the case to move forward. He ruled that the government must present him with the classified documents within two weeks. Apparently he was not impressed with the government's argument, which boiled down to, "You can't prove we wiretapped you unless we admit it, and we won't admit it."
The other interesting twist: Walker is the same judge hearing Hepting v. AT&T, which will decide if the retroactive immunity granted by Congress to telecom companies that helped with wiretapping is constitutional. And since Walker's patience with the government's justifications for warrantless wiretapping already seems to be wearing thin, he might be inclined to overturn retroactive immunity.
Some useful links:
http://static1.firedoglake.com/28/fi.../01/090104-walkercharityruling.pdf (the decision, in pdf format)