Clay Shirky discovers reputation hacking: Many-to-Many: Wikipedia, Authority, and Astroturf. In this case someone may have createed a wikipedia entry to make their project sound authoritative, then they or a friend pointed to it in a Slashdot post. But in fact the project is fairly obscure.
Yes, reputation hacking (false PR) is a real problem. No, it's not new. Shirky cites astroturfing as one antecedent; another he might have mentioned is “reputation farming” — a term surprisingly under represented in Google.
Reputation farming is the practice of creating identities (nyms) in a virtual community such as eBay, and then using the identities in a way that creates a positive reputation for them. In eBay, for example, that might consist of engaging in many small transactions, either real ones or sham ones among the nyms being farmed, in order to build up a good reputation.
One the nym has a high reputation score, it can be sold or used directly to perpetrate a fraud against third parties lulled by the high reputation score.