An article in the on-line magazine Slate by Henry Lanman reports that the US Government has used the concept of state secrets to shield the government from law suits.
Lanman discusses the federal government's use of the doctrine of state secrets to shield itself from embarassment, examining the case of Khalid el-Masri, a German citizen who apparently was grabbed under "extraordinary rendition", held for months, and released only after the government decided they had the wrong guy. Mr. el-Masri's suit was dismissed under the state secrets doctrine.
See also this article in the Washington Post.
Out of the Jungle: State Secrets Doctrine
Political Animal: State Secrets Revisited