With a reach approaching 15 percent of the world's population, Facebook is a thriving media business. In the last quarter alone, it raked in more $1 billion in revenue, almost entirely from advertising.

But to hear some people at big ad agencies talk, it could be a whole lot more.

Here, for instance, is Mike Parker, the co-president of U.S. operations of Tribal DDB, talking about his frustration with Facebook: "For the longest time, we've been trying to call Facebook to do business with them and there's nobody to pick up the call," said Parker. "...They're very focused on the consumer experience, and less focused on revenue and working with advertisers."

Another exec at one of the world's biggest interactive agencies, who spoke on the condition of anonymity, shared that frustration: "We know the reach is there," she said. "The problem is that Facebook isn't willing to do anything different for the client that wants to spend $10,000 versus $10 million."