There is an excellent post on Mashable on The Science of Building Trust With Social Media. The content in this post provides an interesting perspective on what can be achieved through social media and what some of the challenges might be. It is also worth reading the comments below this post to see what others are thinking.
One of the great things about the widespread acceptance of social media is that good organizations, the ones that want to develop and provide good products and services for their customers, have a real opportunity to build trust.