Some of HP's new units have a feature called "scheduled delivery," which lets users schedule printing tasks. For example, one could set the printer to run off portions of a newspaper every morning – and that's where Yahoo's ad network steps in. HP ran two trials where people received content that included ads, and apparently, they were okay with it.
Based on that success, the company may configure printers to use your IP address to lace its "scheduled delivery" service with ads based on your behavior as well as the content itself. Before you go all Facebook on HP, the pilot with Yahoo is reportedly in its early stages and the company acknowledges that "the program has to be done with privacy in mind."