There was an interesting post over at SEO Book titled: Buying Links vs Buying Rankings vs Stealing Content vs Selling Scams
It focuses on the hypocrisy that is present when it comes to link building, buying rank and the morality of it all. Personally I have a problem with Google passing judgement on any site that sells advertising links, saying they are attempting to game the search results but then they go ahead and sell top sponsor ad space to the highest bidder. So how exactly is that providing their searchers with the most relevant results?