“That’s the figure Google (GOOG) vice president Marissa Mayer, who heads search products and user experience, threw out during a Tuesday lunch session at Fortune’s Brainstorm Tech conference in Half Moon Bay, Calif.  How does she put a value on a product that doesn’t directly make money? The online giant figures that Google News funnels readers over to the main Google search engine, where they do searches that do produce ads. And that’s a nice business. Think of Google News as a $100 million search referral machine.”