Note to AC, Christoph, and the author
"it's massively popular. Perhaps you hadn't noticed, it is most useful if you have friends..."
I think you will find it's most useful when you have a null or negative number of friends, but tons of "Lol wassap buddies check that on Utube ROFL", erm, acquaintances.
"The spammers [...] can send emails pretending to be legal documents"
They already do, and it works (at least in the US). Reported here some time ago, if memory serves.
"served legal docs via Facebook"
Via e-mail, you shirley mean? Similarly, in the article you refer to, the bill-dodgers were found because they were friends with one of the waitresses, who gave their names. I'm posting this comment via FaceBook right now, how neat! (you see, I was talking about FB with a friend earlier this year, and it made me think I had to check El Reg from time to time, hence we can legitimately say I'm posting through FB now. Or not?)