On Ártica Online, Jorge Gemetto blogs  [es] about file sharing communities and what we can learn from them:
A common feature of many of these communities is that they are organized around cultural needs  [es]. Preservation, access, dissemination, and distribution at reasonable prices are tasks that the market does not always carry out successfully. Moreover, civil society organizations and governments are limited in their ability to respond to these necessities by intellectual property restrictions.
He then quotes Bodó Balázs , a Hungarian researcher who investigated gated file sharing communities.
In his academic paper, “Set the Fox to Watch the Geese: Voluntary IP Regimes in Piratical File-Sharing Communities” , Balázs makes the distinction between open and closed networks of exchange. Among the former is The Pirate Bay. among the latter there is an unknown number of communities in the shadows that, nevertheless, collectively account for higher activity than open networks. The closed nature of these communities is in many cases a response to the legal persecution from which they suffer.
More on this in the post  [es] on Ártica.