How can companies thrive on social media?

We are particularly interested in hearing from communications professionals and bloggers, but as social media touches all of our lives we recognise that everybody's views are valuable.

Should companies fear social media, or embrace it?  And how should companies react when faced with a social media storm? 

If companies' behaviour is driven by a fear of a social media backlash then what are the implications for customers and for society at large? 

Are there examples of social media being used for sensible debate or is it always hijacked by activists?  How can acceptable online behaviour be encouraged or enforced?