I am seeing more and more companies with increasingly sophisticated products in this space (which Forrester defines as "The ongoing analysis of mainstream media and consumer-generated content to identify trends relevant to a company’s marketing activities and competitive landscape." The early players identified where activity around a given brand or subject was taking place and who was generating the most buzz - the online mavens if you like. They have morphed into solutions which tell us what is really going on - solutions are getting smarter, they can interpret sentiments and many provide the possibility to participate directly into the potentially many blogs without going to each of them in turn. I leave aside the ethical issues that this raises. The truth is though no outsider to an online community will successfully influence a conversation - it's the online equivalent at sitting down at a table full of strangers and starting to talk - the results are predicctable!
A good example of companies and products in this field is Visible Technologies. My company, Wunderman also has an offering. The University of Washington is doing some pioneering research into this field.