There has been discussion on a few sites (all gaming) I go to about companies that hire people specifically for the purposes of guerrilla marketing on online forums.
These employees are expected to develop and maintain between 50 and 100 active identities across any forums that involve their clients products. They maintain these to actually develop the accounts as recognized individuals. That way rather than new poster X making their first post stating some product is really great, GoodBuddy42 with 150 posts is saying it and people are more likely to believe them. If your first and only post is a link its spam. If your 50th post is a link asking are company Y any good it looks like a legitimate post. The objective is achieved though, people click the link, see the product.
Just makes you wonder though, all the examples I found were gaming related but it would be strange if it was just limited to that. It'll certainly make me wonder next time I see someone talking up a product, or offering links to somewhere.
So who do we think is getting paid to visit our forum?