Today, Yahoo started the beta for their Yahoo! Publisher Network (YPN). 2000 betatesters should put the Ads on their sites until the end of the year, after which this form of advertisement should become open to all webmasters. Similar to Googles AdSense, YPN shows relevant textlinks in special ad-brackets and the payoff will be made based on clicks.
The advertisers have the possibility of establishing channels in which they can monitor the success of each of their ad-formats or sites. As in AdSense, there are ten different ad-formats to chose from and both the color of the writing as well as the background can be changed.
One function that is missing at Google is the possibility to move YPN entries to the Yahoo-Search-Marketing-Account (Overture). An extensive article by a betatester can be found at Jensense.