The Wall Street Journal says:

Walter Carl, a professor at Boston's Northeastern University who has studied "word-of-mouth" communication and marketing, says blog-watching services "are very useful for quickly getting the lay of the land" in trends and consumer reactions.

Well, I guess we already knew that but then

Blog-monitoring services typically charge big companies $30,000 to $100,000 a year.

Which seems like extremely good value. I think it might be time for us UK consultants to take our rates up a bit;-)