Morgan McLintic doesn't sound completely sold on this idea, but it seems natural to me - most press releases are ads, and we might as well treat them as such:

PRWeb, an Internet newswire service, has teamed up with Pheedo, an RSS advertising network, to deliver press release headlines in RSS ads. Pheedo already provides context-based RSS ads. Now it will draw content from PRWeb press releases and display the headline and subdeck in those ads. So basically your press release turns into a direct-to-end user advert. The releases selected are context-based around categories such as entertainment, mobile, technology and small business. The theory is that RSS feed subscribers will read the press release headlines and visit the PRWeb site to learn more.