Multi-user games, wikipedia, e-bay, Amazon, Internet Movie Database. They all involve -- in different ways -- the co-creation of value between a platform provider and a social network enabled by that platform. Which raises issues of trust and authority.
From a Guardian article on Wikipedia:
To its fans, it is a fantastic research resource - albeit one that you should use with caution; and an incredible example of what can be achieved by collaboration and cooperation over the internet. To its detractors - mostly those from the traditional world of encyclopedias and librarianship, it is barely worthy of the label "encyclopedia". [Guardian Unlimited | Online | Simon Waldman on Wikipedia's success]