FaceBook would easily be the hands-down top social network when it comes to membership. It is the top social network in Australia, Canada, France, India, Germany, Italy, Spain, the United Kingdom and the United States. It is now ranked No. 1 in Unique Visits (UV) followed by MySpace, Twitter, Flixter and LinkedIn.
The applications at Facebook would be the most visited like those of FarmVille, Cafe World, Mafia Wars and the like. One thing about this applications, if you do not have or could not get real friends that actively participate in them you tend to be left behind or "lose". Eventually you lose interest, or like what others do create another account just to help out on the applications you are into.
Yes, that's how it goes. So, one member can create as many accounts possible in Facebook as long there are "aliases" in the information you put. With that, you will also have to create several email addresses because each account has an email address as user name. Now, if there are statistics that would show how many play or use the applications, there is a good tendency that accurate number of users might not be true.
In fact I have two accounts even if I have many active member friends. The reason is they could only 'assist' one every 24 hours on what you need. At times they can't even give the help or assistance you need. With the other account, I can get exactly what I need. That's how it goes and many members would have multiple accounts. That's aside from orphaned accounts where members forgot or put in a wrong email address then created another or a second account.