I'm not sure how much this has gotten around, but this report, Baghdad nights: evaluating the US military 'surge' using nighttime light signatures, is essential reading.
Basically, several geographers and one political science professor from UCLA used satellite imagery of Baghdad's lights at night to observe the changes in population distribution throughout surge. Overall, a decrease in nighttime lights in Sunni and mixed neighborhoods, while Shia nighborhoods remained the same. In particular, the neighborhoods of East Rashid and West Rashid, historically mixed areas with a slight Sunni majority, experienced the greatest decline in light density.
The outcome seems to have been both a total loss of Sunni population (these neighbor-hoods have produced many of the refugees fleeing Baghdad) and a successful ShiaThe verdict:
strategy of `pacifying' those areas in the city hitherto most hostile to Iraq's largely Shia government. The city neighborhoods east of the Tigris River, many of which were mixed Sunni/Shia and other before, are now heavily Shia. But citywide, there has been a dramatic decrease in the extent of ethno-sectarian residential intermixing. This probably explains the overall lowering of the level of violence. Locally, there is no one left to attack.
Yet, as other Iraqi cities experienced just such an intensification of their nighttime lights, Baghdad had the opposite experience. We interpret this change as indicating that violence has decreased in Baghdad not because of an overall improvement in material conditions or because US troops have imposed a Pax Americana on the city but because large parts of the city have been emptied of their existing populations and sometimes replaced with coreligionists, thus reducing the local stimulus to violence emphasized in the Jones Report (2007).Science, son. Science.