There's another review of The Dark Side, Jane Mayer's exposé of America's involvement in torture, in Open Letters (thanks for calling my attention to it, Sam). Greg Waldmann explains lucidly and in depth a number of Mayer's revelations, including a disquieting link between torture and the case for war presented to American voters:
The most disturbing example of torture’s inefficacy was the "enhanced" interrogation of Ibn al-Shaykh al-Libi, who actually was a terrorist. Bush hailed al-Libi as a model of what "enhanced interrogation" could accomplish. But all the useful information he’d given was given to the FBI, who ran their interrogations normally. The CIA took control, however, and packed him away to Egypt, where he was pressed particularly hard on the subject of Iraqi/al-Qaeda connections. Al-Libi told the Egyptians that three al-Qaeda figures (he used real names) had gone to Iraq to learn about nuclear weapons. It was a fabrication. The Egyptians wanted more, so he made up some more stuff about Iraqi training in bomb-making and biological and chemical weapons. This "intelligence" made it into an October 2002 speech by President Bush, and later into Colin Powell’s famous February 2003 address to the United Nations.