Here's an interesting discussion on the impact of Muslim immigration on Europe. This is an unproven source, and so one would need to verify the facts to fully support the conclusions drawn. But, I have seen similar statistics elsewhere, and so I tend to believe that this post has some truth to it.
The money quote:
In Europe, Muslims already make up more than 25 percent of the population of Marseilles, 15 percent of Brussels and Paris, and 10 percent of Amsterdam, for example. And these numbers are rising fast. Indeed, demographers predict that the number of Muslims living in Europe may double again by 2015. Thus Princeton University’s Bernard Lewis, one of the world’s most distinguished scholars of the Arab and Islamic cultures, recently told the German newspaper Die Welt that: “Europe will be Islamic by the end of the century.”