A friend of mine told me in 2006 that an executive he knows at an oil company was willing to pay 20p-50p for instant (over 24 hours) opinions from a demographically suitable population of people. This is several orders of magnitude greater than the advertising model (with the exception of the usual suspects with billions of page impressions every month). I've argued for many years that the source of value in social networks is behavioural/opinion data, particularly those arising from digital conversations. Selectricity (Voting machinery for the masses) appears to be a robust tool for implementing it. SwarmTeams - has similar utility.
Key to creating a movement at scale is figuring out the model of trust (the exchange of value) and the feedback mechanisms back to the community. Feedback is crucial because prizes and other material incentives won't work (You want me to pay? I want you to pay attention). They are obviously entirely inappropriate for cause related communities.
The biggest challenge brands face in their attempts to create customer communities and engage/interact with social networks is actually changing some aspect of their product, service or policies as result of the feedback they receive. They also must communicate and attribute the benefits of that change back to the community.
To do this well they must start from the inside. That is, create, learn, and experiment with social software. The first step is to discard the company Intranet, a largely one way broadcast medium, and replace it with systems that enable conversations, connectivity and peer-to-peer sharing. This is probably stating the obvious but to participate in a network, a company must itself be network centric. Unfortunately this means taking a conscious decision to dismantle hierarchical organisation. Democratising decision making (crowd sourcing), creating openness and transparency is a big step for large organisations in particular. For most of them, this is still a step too far.
Some more commentary here in an interview with MyCustomer.com.