The diffusion of the Internet has considerably changed the basic principles of information exchange into a structure that is now enabling user-driven information propagation across most markets that was not possible in the previous era of unidirectional mass communication. This study focuses on the submitters' social networks to explain these new propagation processes. Large datasets from a social news site are used to show that it is the size, structure and activity of such networks that mainly influence whether or not certain content achieves a prominent level. Message and content-related factors seem of only marginal importance - at least until the respective content exceeds a threshold of public attention.