For reasons I won't go into, I've just come across this system for monitoring social networking sites called Spark from Spiral16.
If you are ever suspicious that comments on blogs, bulletin boards or networks are from corporate trolls (people posing as members of the public to push the company's agenda) then you could be right.
This handy film shows you how to track and interact.
A few year ago The Guardian ran an article by George Monbiot called: "The fake persuaders: Corporations are inventing people to rubbish their opponents on the internet."
If you don't think corporations would be so sneaky, then take a look at Nestlé's spying operation. Attac Switzerland has just published a book about the spy that infiltrated the editorial board for a book being put together on Nestlé.
The book is in French. You can find information in English on the spying scandal at: