Last August, Moqtada al Sadr declared a unilateral ceasefire for his Mahdi Army, and the ceasefire has been observed. But there is increasing evidence that the Mahdi Army has completely infiltrated the Iraqi security forces, and is waiting for U.S. forces to diminish before re-emerging as the major force in Baghdad and southern Iraq. Much of the surge's success in and around Baghdad has been facilitated by the sectarian cleansing of Sunnis from their homes; where there were mixed neighborhoods before, now there are none. Violence is down when all of your neighbors are the same religious sect as you (see Northern Ireland and Bosnia).
This displacement of Iraqis from their traditional homes, neighborhoods, and villages, along with the emigration of 3 million from Iraq, is perhaps the most significant human tragedy of post-invasion Iraq. It's something that this Assministration will be held accountable for ultimately.
