Question: social media and brand relationships

My chum Chris has asked this question:

We all believe that people's relationships with brands are changing as a result of Web 2.0.

But what's the real evidence for it?

Evidence that's more than anecdotal? Evidence that will stack up with a numerate skeptic?

My first thought are datasets like the Edelman Trust Barometer which has plotted the long-term decline or trust in companies and their activities…Prahalad laid out the argument here…

But what's the real evidence for it?