The above gif comes from the Vincos Blog and shows the dominant social network by country across the globe from June 2009 to December 2012.
Note the consolidation in the number of dominant sites over the 4 year period from 17 to 5.
Facebook has now established its leadership position in 127 out of 137 countries analyzed. As social media moves from infancy into adolescence this pattern is important to note as it follows a similar trajectory to other industries throughout history. You can use search as an earlier example. At first, a large numbers of smaller players vie for position and as time goes by, a smaller number of the most successful ones come to dominate.
My guess is that we are also observing a consolidation across more specialized, vertical, networks such as LinkedIn for professionals and Yelp for recommendations.
Good news for the leaders.
$FB $YELP $LNKD