Clinton Watts looks at the Sinjar records and concludes:
Western fixation with AQ’s propaganda has resulted in over-focus on countering media outlets that likely have limited and at best a secondary recruiting impact in high foreign fighter producing cities and countries. While AQ mass media propaganda is an important factor in the war of ideas, it should be addressed more in Western counterterrorism efforts in Western countries where socially isolated second and third generation Muslims and Western converts have limited direct access to militant ideologies, limited access to veteran foreign fighters, increased access to the Internet, and a propensity to access militant websites. The two non-Western exceptions to this might be Saudi Arabia and Morocco, which appear to have sufficient access and desire to utilize militant websites. However, the plethora of former foreign fighters in Saudi Arabia and Morocco is far more likely the radicalization culprit with the Internet acting as a distant second factor.
The West should fear instead what it cannot see on the Internet: the day-to-day interactions and subsequent radicalization occurring when veteran foreign fighters encounter young recruits in living rooms, ideological centers, schools, workplaces and neighborhoods in flashpoint cities.
The whole shebang, including discussion on data, plus country and city analysis, can be found here.
For comparison, see Andrew Exum’s take on what happens when Omar comes marching home.