Having lived in and around Paris, I feel I should comment on the riots there. I met alot of North-African emigrees in France, mostly algerians; on the whole they were poor and lived in government-built housing projects called HLMs. I doubt there's a big religious cause to these riots, as most of the Muslims I encountered were not overly religious -- rather, this is probably culture-based. Frankly, most white people in France don't like the arab immigrants. The oft-lampooned ultra-nationalist (read racist) politician Jean-Marie Le Pen is strongly supported by 1 out of every 8 Frenchmen, and 1-in-3 Froggies have a favorable impression of the man (Le Pen is on the record as saying that the Holocaust is a detail of WWII and that racial equality is absurd.)
I'm saying that there's a pretty huge cultural divide in France -- exacerbated by the welfare-state mentality. The confiscatory tax rates and commensurate goverment spending have led to anemic economic growth and -- more critically -- french citizens are totally dependent on their government to provide a life for them. The net effect is entrenched and multi-generational poverty for the great majority of Arab immigrants.
Thus, a great deal of pent-up anger and frustration.