Seeking to bring more control/choice to advertiser-buyers of its AdSense program, Google has offered advertisers the ability to bid for inventory directly on particular network sites. This capability is one of the ways that competing contextual ad providers Kanoodle and Quigo have been selling against Google — more control, more transparency.
This move follows on the heels of ongoing refinements for AdSense and specifically Google's willingness to separate bidding for AdSense and AdWords. Contextual ads traditionally haven't performed as well as paid search ads.
John Battelle believes this will create controversy with many publishers.