I have no way to confirm all this independently, but I work on the Iraq program and things don't sound good. I just got an email from a colleague who said that power in Basrah is completely cut and has been for hours. They have no idea when it will be restored. All stores are closed, as are markets and no movements are allowed. Gunmen roam the city at will. The Iraq army is not much in evidence. There was a report that 17 US soldiers has been captured and were held hostage, but this has not been confirmed. I can't imagine that it would have happened without a major fight, but details are unavailable. If there is a news blackout and fighting continues for the 72 hour "ultimatum" this could be a prelude to something unpleasant in the extreme.
One issue is that with the (relative) increase in security, people were not prepared for a long siege and so don't have lots of candles, food, water stored up, at least not in amounts to last for more than a few days. My guys don't sound desparate, but they are clearly worried.
The problem is that the Maliki government is declaring war on the Sadr organization and the Badr brigades, both of whom are in the government. If they withdraw, which heavy fighting will lead to, then the government falls. Then all hell breaks loose, with fighting spreading to the big cities, especially Baghdad, and no government with the power or popular support to stop it. The US would have to do soem serious fighting to calm things down. Plus the US is planning their final push into Mosul to root out the insurgents that have taken up residence there as a result of the Awakening movement and the surge, so that could be VERY ugly. Pray for peace.