I know that at this point I've basically beaten the social networking horse to death but I want to offer one more thought on it and then I'm done. I swear.
The more I think about social networking products that are intended to expand and strengthen social connections in the name of business opportunity the more I think that they misunderstand the fundamental nature of social capital. Social capital is just that, "capital." If you aren't careful you can spend it all up. Sure, there are some relationships that will be more resistant to fatigue than most -- for example, I am sure that I can make a lot of introductions to my dad before he stops taking my calls. But some relationships are far more tenuous. If you have a good conversation with a potentially helpful business contact at a conference, he will probably take your call or read your email the first time you reconnect with him. But that relationship is pretty fragile and if your initial post-conference contact with him isn't at least mutually beneficial, that relationship will be spent before the second email. Even relatively strong relationships can be taxed if they are over-exercised.
If I were to bother the same person for multiple introductions serving only my interests, even a good friend is going to get sick of hearing from me pretty quickly.
I frankly think that social networking is close to a zero sum game. We can only maintain a relatively small number of strong contacts and a somewhat larger number of weak contacts. Relationships are maintained through interaction -- we call, email, have lunch, etc. Such intense relationship take time and energy -- perhaps we can keep up with a few dozen people that closely, but certainly not hundreds. Moreover, given the sustained nature of close ties, any attempt to increase the circle of strong contacts will either weaken all of the strong relationships or marginalize some relationship that would otherwise have remained close. Similarly, attempts to increase one's circle of loose relationships will either weaken all those relationships to the point of having little value or replace old relationships with new ones.
It is conceivable that technology could make us more efficient and therefore increase our universe of relationships (I am sure that I'm able to stay in closer touch with many people thanks to the use of email -- after all, it is a little difficult to get away with calling people to chat at one in the morning). But I believe that increase is marginal. We are all able to maintain a finite number of relationships, many of which are fragile. As social networking software grows more prevalent and an increasing number of people attempt to draw upon our social capital to make introductions, entertain business propositions, pass along resumes, etc., I believe we will all grow more guarded with our time and our relationships. If social capital is indeed capital, we will all soon be more careful about where we spend it and on whom.