The New York Times details a history of the phrase, “mistakes were made”, which has seen some heavy use in Washington since the era of Tricky Dick the First. I particularly liked this zinger from the final paragraph:
The nonconfessions inspired William Schneider, a political guru here, to note a few years ago that Washington had contributed a new tense to the language. “This usage,” he said, “should be referred to as the past exonerative.”