I'll defend the post against these counter-arguments in a couple of ways. Firstly by talking about the nature of metaphor and secondly by exploring the role of sharing.
I knew Stephen, being the lovable old socialist he is, wouldn't like an economy metaphor. But we don't have to like, or take all of the elements of a metaphor, in order for it to be useful. Metaphor is a form of mapping across domains, from a source domain (in this case economy) to a target domain (in this case PLNs), with the intention that the source domain will help us understand the target domain better. Of course, no metaphor is perfect, indeed can not be, otherwise it would be the target domain. So we should only map across certain elements.
Viewing something as an economy has some potential benefits, but we must always be careful not to extend the metaphor too far. For example, we can view nature as operating some form of economic principles (indeed Malthusian economics helped Darwin formulate the theory of evolution), but that doesn't mean we extend the principles of intentionality from the agents - we don't anthropomorphise animals and plants as selling and exchanging goods.
So when I said we could view PLNs as a form of reciprocity economy, I was suggesting that we build up a sense of identity capital, and that reciprocity is the 'currency' through which exchange is realised. I didn't mean to suggest that, for example, we set out to utilise our personal network for monetary gain. In this respect I think the metaphor needs flushing out, but I think Stephen's argument that I interpret a network solely as a value proposition is simplifying it.
Secondly, Stephen said in the comments and in the post that it is about sharing, which is a completely different concept. I'm not convinced they are as widely separated as he suggests. I tried to make it clear that I was proposing a more subtle form of reciprocity - it is far beyond a simple 'I'll do something for you if you do something for me' kind of exchange. And I was talking about the manner in which one develops a personal network, which adds value to your life. This, it seems to me, goes beyond merely sharing. I admit that sharing is the base, the sine qua non, of your network, since if no-one shares then you cannot even begin to establish a network. But, when that network becomes meaningful is when you form relationships, and have exchanges. It is when an element of reciprocity is added over the blanket sharing that the network attains a more significant role in your life.
Sharing is to reciprocity as gold-mining is to jewellery making - the latter cannot exist without the former but it is the latter which adds real value and interpretation.
But ultimately metaphors come down to choice - they aren't really right or wrong. Often it is by arguing around the metaphor itself that we come to understand the target domain better. Some people will find the reciprocity economy useful, others not. I'm still not sure myself how useful it is, but for the moment I think it's worth kicking the tyres (to use another metaphor).