[. . . then wheezing and coughing, like a *real* "old person."]

...is if someone who knows you signs up for FB and says they know you.

For example, FB has a function when you join where you can give them a list of email addresses and they'll tell you which of those addresses are on FB. But for the ones that aren't, they stay in your account, so when someone on that list joins, they automatically suggest you connect.

I honestly don't understand a lot of it once it gets into the math/stats. I just know the mechanics of it from pitches I've participated in. They can figure out that X number of people are connected within N degrees of someone on your e-mail address book, and then construe that to figure things out. It's not who they know you know. It's who they know the people you've already said know or probably know. And it goes even further than that.

The fun thing about a lot of it is, until the sites like FB and such really got going, most people involved didn't even really realize it was going to happen.

--
Sometimes I rhyme slow sometimes I rhyme quick.

but have you sent Angel emails from that account? I believe LinkedIn looks at your contacts with permission and recommends folks. There are also some pretty sophisticated social networking models that companies like these use. LinkedIn, for example, suggested a secretary at a client of mine from 3 years prior whom I never exchanged emails with and had no other links for in my profile.

If you are really interested there are some great books on the subject of analytics that touch on some social media stuff. Competing on Analytics is decent and SuperCrunchers is quite good.