The idea to mirror real world personal networks has taken off some years ago. I liked the idea from the beginning. If it would be possible to organize business contacts in an online forum it widens your personal reach tremendously. Services likes Plaxo help keeping your address book up to date. But the management of your contact list was still to you.
Another leap forward were services such as Polypol. It is designed to service rather closed communities. It keeps alumni or sport organizations up to date about its members. It could be used as a proper network for business relations but hasn't really been positioned in this direction.
A big leap forward came with LinkedIn, co-founded by a friend of mine. It took processes from a real world cocktail party into a piece of software. It's not just storing address books; it's the possibility to make introductions to members of the network via personal referrals. This a huge potential, as you can see the short CV's of all members, but you only get in touch via a trusted route (the connections). Combined with some good search capabilities it's very helpful. Joi Ito has discussed pro's and con's intensively.
However there are some problems remaining. First personal networks typically have a fine system of 'intensity levels'. Friends and close business partners can be approached very differently compared to people you just exchanged a card with. This is not mirrored so far and really decreases the value of the application in my eyes as this limits the usage and keeps myself in MS Outlook. Second European business networks are even more based on trust and long-term relationships. For most people in business keeping another up to date CV somewhere is more a threat than an opportunity. The value of a (widespread) network is generally less appreciated. In conclusion I think it will take some time, but online business networks or social software will makes it's way. It might be a necessary tool for everyday work and life in some years. If there is a real business case behind has to be explored.