I have some words of advice for some of the blog networks out there. You may be wasting your competitive advantage by sticking to the straight ad network model. Figure out some new ways to help to get your clients to engage your audience in a more meaningful fashion. I'm not suggesting that blogs or blog networks cross the advertising/editorial wall. What I am suggesting is that run-of-the-mill ad units aren't the answer to every communications problem, and if your answer to every RFP is a smattering of banners and skyscrapers (or steering the client toward your self-service interface), you're not taking advantage of the deeper level of engagement you have with your audience. And you're not taking advantage of everything conversational marketing has to offer.
Some clients need consultative help to figure out how to engage your audience once they've gotten their attention. With their online marketing efforts, most marketers have placed their emphasis on quantity and not quality of engagement. A great way to differentiate yourself when pitching against ad networks and the Big Three is to concentrate on the quality of the engagement and what the marketer ought to do once the audience is engaged.
Some of the things you might want to discuss with potential clients is the notion of how they can speak credibly to your audience. Perhaps that discussion might include how a marketer might provide a forum of their own, how they might respond to comments and how they might join the conversation. The big websites and ad networks won't be able to speak credibly to that. That's one of your competitive advantages.