Via Jonathan Edelstein, I found Randy McDonald's France, its Muslims, and the future, which examines and debunks the idea that France will be taken over by its Muslim population. Randy examines the actual statistics on demographics and religious observance of French Muslims and compares it to other immigrant groups, in France and elsewhere.
His conclusion:
France’s problem with its nominally Muslim minority in the early 21st century isn’t a civilizational clash, any more than the United States’ problem with its nominally Catholic minority in the early 20th century was. The French problem isn’t whether or not it will be a Western country, or a democratic country, in a half-century. The French problem is how a large immigrant population, already fairly highly assimilated in the cultural sense but concentrated in certain immigrant ghettoes where assimilation in the socioeconomic sense is more problematic, will be integrated into itself. There’s no particular reason to think it will fail, given France’s own past immigration successes; there’s also no reason for complacency, given France’s problems with youth and immigrant employment, and with social exclusion. It's a touchy situation, but like graduate school it's far more difficult to fail than it is to muddle through and succeed.