So far, U.S. soldiers have been lucky, if you can call it that. Only one U.S. soldier has been confirmed dead, but five were wounded in Najaf, another seven were wounded in fighting in Sadr City in Baghdad, and a U.S. helicopter was downed, the crew taken away wounded. Some clashes have also been reported between Sadr supporters and British troops in Basra.
Likewise, Iraqi police and army forces have also been targeted in attacks that have caused considerable loss of life and wounded, effecting both soldiers and Iraqi civilians.
The question at this point is, how big will this uprising get? Ginmar calls it "a smaller scale April", referring to the uprisings that killed 135 U.S. soldiers that month, the costliest month of the war so far. I think it's premature to say that this is going to be a smaller scale event, however, for a few reasons:
1> Many Iraqis will be going to Friday prayers at mosques all throughout Iraq tomorrow. What they hear from their local religious leaders will have a considerable connection with how major this uprising is. The uprising in April got considerably worse when Iraqis, sympathetic to the horrors of Fallujah, were swayed by local preachers throughout the country. Many of those arguing for united opposition then were supporters of al-Sadr, whose April uprising fed upon incidents in Fallujah, just as much as incidents in Iraq's spiritual capital of Najaf. It is entirely possible that Sunni religious groups, such as The Association of Islamic Scholars, will speak out in support of the Sadrists, returning the favor, you might say, for their support in the past.
2> Even if the size of the uprising is smaller, there is reason to suspect that the techniques used by the Sadrists will be more effective. In the April uprising, the Sadrists showed themselves to be absolutely terrible shots, and were slaughtered by the dozens. Repeatedly, they failed to exploit potential U.S. weaknesses, throwing their bodies into the meat grinder. Already, however, we have seen different -- and arguably more effective -- tactics than in the first uprising. Carbombs targeting police stations. Effective targeting of U.S. helicopters. Explosive-oriented ambushes. Hostage taking. There is even a strong potential for suicide bombers and females to be involved in the insurrection, making it hard and costly for U.S. troops to trust the local citizenry, and possibly further alienating them from mainstream Iraqis. All these techniques exploit U.S. weaknesses in this kind of fight, as U.S. military forces do better when they can gain good intelligence from the locals and have large formations of enemies to target. As we've seen time and again, failure to have good intelligence on enemy positions leads to civilian casualties, which can potentially incite Iraqis and make the uprising worse, as we have previously seen in Fallujah.
3> Infrastructure attacks. Arguably the greatest victory for the Iraqi resistance in April wasn't that the U.S. lost over a hundred soldiers that month. Rather, it was that truckers, foriegn businesses, and reconstruction workers fled Iraq, setting back the reconstruction in Iraq by months, damaging power output noticeably, and causing serious supply problems for the U.S. Army that, had they persisted, would have caused serious problems. These supply problems contributed greatly to the U.S. making peace with the Fallujah resistance and the Sadrists, largely on their terms, leaving Fallujah to the resistance and Najaf to the Sadrists. During the April uprising, soldiers were forced to resort to MREs (meals ready-to-eat) as supplies weren't arriving and foriegn help was in short supply. Some units also faced disconcerting water shortages. That, incidentally, is a huge consideration in this uprising, given the summer weather. If Sadr supporters can effectively target the infrastructure that delivers water to the U.S. troops, primarily targeting their efforts towards cutting off U.S. troops and supplies with improvised explosive devices along with targeting those who deliver U.S. supplies, they might have a higher degree of success than they've had in the past.
No, I don't think the U.S. Army is going to dry up and blow away, but it does seem reasonable to assume that Sadr's supporters will learn from past lessons. For now, though, we're in a waiting game. Hopefully, things won't get as bad as they did in the past.