One of my consistent themes has been the power of a group to get stuff done, and the ways the web facilitates, and empowers the processes needed to get the stuff done by the group.
However, which is the chicken, and which is the egg?
There are no groups without members, and the “members” need a motivation to form, be a part of, and contribute to a group, in a way that enhances the outcomes for the group.
As a marketer, it is our task to find that motivation, and use it to build a network, group if you like, of those to whom the value proposition of the product/service being marketed adds value.