Interestingly enough, RAND published a paper comparing the assimilation of immigrants in France and America back in July '04. Due to recent events, they've put it back on their homepage:

Assimilating Immigrants: Why America Can and France Cannot
The large-scale immigration of Mexicans and other Latin Americans into the United States has stimulated a debate on America’s ability to assimilate them. A parallel debate in Europe, particularly France, concerns the ability of that continent and that nation to assimilate the similar ingress of Muslims from North Africa and elsewhere. This occasional paper uses the history of mass immigrations into the United States to examine the two current streams and the two debates. It concludes that today’s Mexican inflow differs little from past mass immigrations into the United States by the Irish, the Jews, and the Italians and that assimilation should be as successful as in the past. France, however, while it has successfully assimilated a wide variety of individuals, has had no previous mass immigrations, and its current direction is likely to lead to increasing problems. The paper suggests a steady as she goes course for the United States, and some policy changes that may help France cope.