The tech-savvy ex-hipster geek-trash I know in Houston all love Ok Cupid. But they use it heavily for the sort of social networking that Facebook is suppoed to be for. (It's apparently better than Facebook for finding people with similar esoteric interests.)
On the flip side, Facebook & Friendster started out as surreptitious dating sites. People went on there to figure out who among their friend's friends were cute enough to date.
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).
On the flip side, Facebook & Friendster started out as surreptitious dating sites. People went on there to figure out who among their friend's friends were cute enough to date.