Josh Bernoff, one of the co-authors of Groundswell, the best-selling Forrester book about social media technologies, talks about how social media fits into the mix during an economic downturn.
He argues that social media communities/blogs are relatively inexpensive compared to many other marketing activities and can help companies generate positive word of mouth. If you haven't read the book, I'd strongly recommend it.
http://loispaul.typepad.com/blog/2008/10/an-chat-with-groundswell-author-josh-bernoff.html
www.itsopen.co.uk