An excellent read form HBR Analytic Services:
The New Conversation:  Taking Social Media from Talk to Action

From the executive summary:
– many still say social media is an experiment, as they try to understand how to best use the different channels, gauge their effectiveness, and integrate social media into their strategy.
– many companies have yet to capitalize on the ability to not only listen to, but analyze, consumer conversations and turn the information into insights that impact the bottom line.
– Only a small group — 12 percent — of the companies in the survey said they felt they were currently effective users of social media.

Lots of excellent charts, including this one (click to enlarge):

And, this one:

The opportunity: