It sounds like the move against al-Sadr and the insurgents in Najaf has begun.

Thousands of U.S. troops and Iraqi soldiers began a major assault Thursday on militiamen loyal to a radical Shiite cleric in Najaf, with explosions and gunfire echoing near the holy city's revered Imam Ali shrine and its vast cemetery.

Although it is often an unreliable source, Debka had this interesting tidbit about the insurgents within the shrine:

DEBKAfile’s military sources report Najef standoff nears climax. US Marines-Iraqi National Guards cordons thrown up around Shiite city - one external, second enclosing Old City where fighting rages around Imam Ali Mosque. Reports Sadr has booby-trapped shrine and threatens to blow it up with 2,000 militiamen inside if US-Iraqi force storms in.

If this action will result in the net loss of 2000 terrorists plus their leader, then it is long overdue. It is curious that so many predict the imminent Shiite revolt should the Imam Ali Mosque be damaged. Damaged, because Sadr cares more about his own body than this site revered by Islam - and if the Debka rumor is true, it might be intentionally destroyed by al-Sadr in a final act of martyrdom. I presume that any explosion would be blamed on the US and Iraqi forces outside the shrine and not on those within.

The Mosque link above is interesting not only because of the pictures it contains but also because it explains the history of the shrine. It also contains this interesting tidbit:

In 1991, Saddam damaged the Imam Ali Mosque because most of the people who rebelled and were part of the uprising against Saddam Hussain's government, were hiding in that mosque and they were taking it as a place of leadership. And so the Republican Guards fought the people, damaged that mosque and killed all the people who were inside. General Wafiq Al Samarae [the former director of the Iraqi Intelligence Service] admitted in his book (Eastern Gate Ruins) that Saddam's regime used chemical weapons against Iraqi people in the holy cities of Najaf and Karbala to crush the popular uprising of March 1991 which followed the defeat of Saddam in invading Kuwait.

History does seem to repeats itself.