As a new set of community technologies develop on the Internet, we should not be surprised to discover that the sociology of how we buy will come to resemble pre-industrial markets. In the post-industrial world, reputation, relationships and recommendations can come at any time from anywhere to affect a purchase decision.
Before you entirely discard the notion of advertising, however, it is worth noting that it can and will change. Companies will recognize that there is a conversation going on in the marketplace that they should join, not dominate. And once a company has become a part of the conversation, conventional one-way advertising can draw attention to the conversation and to the company's participation.