@cicerone imposter,
I disagree.
While Islam is often referred to as "the fastest growing religion," the accuracy of this claim is dependent upon one's definition of "fastest growing."
Assuming, however, that Islam is the "fastest growing religion," there is absolutely no reason to believe Christianity or any of the world's other great religions will become a "has been" in the near term.
In addition, there is little to no reason to believe that the speed of it's growth has anything to do with praying five times a day or a perceived intensity of faith.
As you know, Christianity is currenly the largest (in terms of estimated adherents) religion in the world. Approx 1 in 3 people self-identify as Christians, while 1 in 5 self-identify as Muslims.
Focusing only on the demographics of The United States and Western Europe may lead one to the conclusion that the worldwide dominence of Christianity is in rapid decline, but that would be looking at only a corner of the entire picture.
Throughout the world, Christianity is growing at a rate of about 1.4, despite the acknowledged and somewhat steep decline in adherents in developed nations. The latter trend, of course, has nothing to do with the specific teachings of Christianity, but illustrates that the more advanced and sophisticated a society become, the less the members' interest in institutionalized religion.
What nation, in which Islam is the dominant religion is as advanced and sophisticated as the US and Western Europe?
Christianty is steadily growing in the region of the globe with the highest population growth: sub-sahran Africa. In all of Africa, Islam leads at 45% of the population with Christianity close behind at 40%
At present the growth in Islam is due primarily to birth rate, while conversion remain a significant driver in the growth of Christianity.
In South America where there is a positive birth rate, Christianity is the religion of approx 90% of the population.
At current growth rates (with that of Islam being in the area of 2.3% and Christianity at 1.4%), the number of Christians in the world will still exceed the number of Muslims in the year 2050, which hardly describes a "has been."
I don't care which religion, if any, "wins out," as long as its adherents act civilized.