U.S. troops strength in Iraq will be down to 120,000 by the end of October. That will continue to decline, as the violence in Iraq does. For example, the standard U.S. benchmark of hostile activity in Iraq is the number of daily attacks. This peaked at a little over 200 a day in the Summer of 2007. This activity has since declined to about 70 attacks a day in February last year and, in August, 2009, to 20 attacks a day.
The attacks most likely to made the news are the large suicide bombs, usually directed at civilians. These peaked in March, 2007, when there were 130 of them. This has since declined to less than 40 a month (including many than only kill the bomber, because of the lower skill levels of the bombers). Moreover, many more of the bombings are smaller, usually individuals wearing bomb vests. For a long time, these were a minority of the attacks, usually 5-15 a month. But in the last few months, they are now more than half the attacks. Until last year, most of the attacks were roadside bombs (and most of these "attacks" were actually bombs that were detected and destroyed.) What we normally think of as an "attack", as in someone shooting at someone, for firing rockets at a base, were always a minority of the attacks (usually a third or less.)
There are still terrorists in Iraq, but most of those still at it are either a small group (a few hundred people) of fanatics who will keep at it until killed or caught. More dangerous are the former terrorist support staff, who can be brought back into action if the paycheck is large enough. These veterans are responsible for most of the carnage this year, and there are thousands of these guys around, nearly all of them officially "retired" and working legit jobs.
U.S. commanders see ethnic and religious differences as the biggest danger. Shia and Sunni groups (tribal, political) are still very hostile to each other, and not reluctant to use mass murder to make a point. The Arabs and the Kurds are willing to die for control of oil fields in the north. Then there's the corruption, especially all those politicians and businessmen trying to steal the oil revenue, or anything else that's available.
The sad part of all this is that Iraq is not much different than its neighbors, who are more peaceful because all the groups that still hate each other, have worked out temporary truces. The entire region is a powder keg, ready to explode with the right combination of bad luck and bad decisions.