My ex-girlfriend used a second Facebook profile to earn rewards in the *ville games (or something, I have no idea how those games work). Truly fake secondary accounts like that are probably quite common given the popularity of those games. All of this just demonstrates that using "monthly active users" as a metric is meaningless and Facebook need better and more well thought out metrics.
This is a huge problem I've harped on before, that will get worse in the future. We've all seen Zynga get buried the past few weeks; what happens when large flows of people stop playing these games? It's much harder for the people still playing to achieve some of the "Ask 10 friends!" objectives that are so prevalent.
This is very common on the Zynga *ville game scene. There are massive rewards for sharing (ie. spamming) your friends and having them click links. So it's better to spam yourself with two or more fake accounts to get those rewards.
