The value of a reader in an author pays publishing model
In many respects the changes in online communication and collaboration have been the leading edge of what latter is tested by the scientific community. I regard sites like Digg, del.icio.us, blogger and other related sites as experiments from witch we can learn about using the internet to make scientific communication and collaboration more efficient. In that context I think there might be an interesting analogy between a study (PDF version), pointed by Nick Carr discussing the value of a free costumer.
In this study the authors created a model to analyze the "profitability of costumers in a networked setting". One example of this type of setting are the auction houses were two distinct users (buyers and sellers) exist. Buyers do not pay anything to the auction houses but provide an obvious value that is, as they say, difficult to quantify. In their analysis they estimated that in this type of network setting the value of buyer is actually higher than the value of the seller (the one that actually pays to use the service).
How might this relate to scientific publishing? In the current model of a journal like PLoS or similar journals there are two very obvious "costumers", the author (that pays to have the article distributed) and the readers, that pay nothing to get access to the journal. The other main publishing model is the opposite, the authors pay nothing (or much less at least) and the readers have to pay to access the journal. It might be that in the different models the publishers might have to direct their efforts differently. In a journal like PLoS ONE were the quality of the service might actually improve with the participation of the readers (annotations/discussions) I would think that the value of the reader is likely much higher than the paying costumer (authors). It would interesting to read a similar study directed at the economics of scientific publishing.