The Iraq casualties site gives these numbers for the past fifteen months (though the compilers admit that they are counting only a fraction of the real casualty toll):
Iraqi Security Forces and Civilian Deaths.
It is true that the September '07 numbers are lower than at any time since June of 2006. But it is also true that June of 2006 was a fluke, followed by an alarmingly rising death toll in August and September. Deaths also fell in 2006 during Ramadan (which started 11 days later being as it is on a lunar calendar) compared to the previous period. Despite the widespread conviction that Ramadan is an especially violent month, in fact it is a time of fasting, prayer and family get togethers and not at all propitious for sneaking off to blow things up.
The other thing to observe is that the September death count for Iraqi civilians and security forces is 842! This is a number at the upper limits of averages for months during the year 2005. If you go back and look at the headlines and commentary in 2005, nobody thought that level of violence acceptable. That is, so far the numbers have fallen back down to merely horrible from having been, in much of 2006 and 2007, truly monstrous.
As many have pointed out, there are now many fewer mixed neighborhoods in Baghdad, so that faction-fighting and death squad activity at that level has declined, because it was aimed at ethnically cleansing the neighborhoods. Baghdad was about half Sunni and half Shiite in 2003. By January of 2007, it was 65 percent Shiite. It is now 75 percent Shiite. A lot of the violence in the figures above was committed in the subterranean War for Baghdad, which the Sunni Arabs decisively lost in the past eight months. The American troop escalation does not appear to have interfered with the displacement of tens of thousands of Sunni Arabs. In fact, my guess is that it unwittingly abetted it, since the Americans disarmed or chased away the Sunni Arab militiamen who defended their neighborhoods from the Shiite onslaught. When the Americans weren't looking, the Shiites took advantage of this weakening of their foe to push Sunni Arab families out of mixed neighborhoods.
By the time Iraq falls apart, sometime after spring 2008, Baghdad will cast its lot with the Shi'ite successionists and not the center of the country. Anbar and Sala an din provinces seem thoroughly Sunni now. Ninawa will be by the time the Kurdish boundary is settled. Diyala seems to be the only truly ethnically mixed territory left.