I'm quite impressed by Facebook's friends suggestions, I discovered a lot of friends thanks to it. I'm not sure he received this suggestions solely on his emai

I'm quite impressed by Facebook's friends suggestions, I discovered a lot of friends thanks to it. I'm not sure he received this suggestions solely on his emails contacts as I haven't allowed Facebook to access my email contacts and I could find most of them in my suggestions anyway. I suspect that they also log when you view someone's profile and use this metric to offer better recommendations. Anyone know more about how it works and what data they use ?