There is a strong possibility Yahoo may enter the contextual advertising market in order to compete with Google's own Adsense program. Google has had tremendous success with Adsense which consists on displaying keyword-targeted ads on third party websites, giving independent webmasters the chance of reaching a wide arrange of advertisers. Yahoo recently announced the merger of various search divisions into Yahoo Search Marketing Services. An API was released as well so that developers would use it and design personalized programs with other Yahoo Services.
Yahoo has also opened a section offering SEO (Search Engine Optimization) and SEM (Search Engine Marketing) called the Small Business Resource Center. Finally, a sub-domain was registered as well "publisher.yahoo.com", which speculates that Yahoo! will indeed enter the Contextual Advertising Market as a competitor against Google.