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Yahoo has joined Google in offering self-serve RSS ads, writes Adam Kalsey. Participants in the Yahoo Publisher Network can place Yahoo Search Marketing ads in their RSS feeds." The ads that appear may be relevant to a specific article or post, or to your content in general," according to an email sent by Yahoo to member publishers. "Now that Yahoo and Google, the two largest self-serve online advertising companies are in the game, there will need to be some changes for pure plays like Pheedo, FeedBurner, and Feedster," Kalsey writes.

He provides a rundown of how Yahoo's RSS ads work and compares the system with Google's and some of those pure-plays.