At least in the United States.
Mark Zuckerberg may be a bit concerned about the recent statistics of your site in the U.S.. According to a report by analyst firm comScore, in the period from March to May fell - a slight, but still - the number of unique U.S. Facebook users. In March, there were 158.93 million in April alone 240 thousand. less, and last month the figure was 158.01 million. Since the tracks it to comScore, Facebook does not have fared so badly in the U.S..
This is clearly a disaster, though probably a downward trend in the U.S. will be maintained in the coming months. It should be borne in mind that Facebook still functions in many other regions of the world and conquer other countries on a regular basis, recruiting millions of new users and compensate each other in this way worse in the U.S..
Facebook kills out to the threshold of one billion unique users around the world, and probably soon will be able to go far to cross. So far, nothing indicates an imminent decline in popularity largest social network. But in five years this could change.