Well now, this is interesting: Petraeus on the Sadr movement:

General David Petraeus, the commander of U.S. forces in Iraq, said Shiite cleric Muqtada al-Sadr is a "leader of an important and legitimate political movement," urging the Iraqi government, in whose selection Sadr was a kingmaker, to recognize and deal with it.

"I think the way, the best way to characterize Muqtada al-Sadr is that he is the face and the leadership of a very important and legitimate political movement in Iraq," he said."

Muqtada, the leader of the Sadrist movement, is the son of Grand Ayatollah Muhammad Sadiq al-Sadr, who was assassinated by the former Iraqi regime's intelligence agencies in early 1999. The elder Sadr was Marja al-Taqlid, source of emulation, for Shiite Muslims. Muqtada is also the leader of Jaysh al-Mahdi, or the Mahdi Army, militias, which he founded in July 2003 as a military wing for his movement.

"Sadr's movement is part of the alliance that elected the government of Prime Minister Nouri al-Maliki," Petraeus said during a joint press conference he held in Washington on Thursday with U.S. ambassador in Iraq Ryan Crocker.
Much more from both Petraeus and Crocker on Sadr's movement in 10 April press conference in DC. You can see it on CSPAN's website - scroll down to "Petraeus and Amb. Crocker News Conference on Iraq (April 10, 2008)".

The Muqtada question is right at the beginning. Crocker and Petraeus both emphasize the Sadrists' legitimacy, say that that Sadr is not an enemy of the U.S., and Petraeus even calls on the Iraqi government not to "back anyone into a corner".