Your last point raises an interesting question - when the current business model of social networking sites is "keeping in touch with people you know", might a future business model be:
"Helping you find people you don't know but will find useful - for work, dating or sports"?
For the dating piece, wonder if a "bounty" model might make sense. i.e. I will pay a matchmaker $1 to introduce me to a potential match (if I agree it is a good match based on some preliminary info about the person).
