Brian Solis’s ebook on customer service provides some good examples of organizations using social media to reach out for customer service.

From the book:
“You can bet that for every inbound customer inquiry, that there is a significant
 percentage of existing and potential customers actively discussing the same
 topic out in the open, simply looking for guidance, feedback, acknowledgment,
 and/or information. And usually, these discussions transpire without company
 participation, leaving people to resolve issues and questions on their own.”

Some organizations mentioned: Southwest, Freshbooks, ACDSee