KOHLER, Wisc. - The answer was all around them. Five panelists sat onstage considering the problem: "Proving Social ROI to the CFO." The occasion was the MediaPost Brand Marketing Summit. The venue was The American Club, a resort where the WASPy tradition infuses every cubic inch of the sprawling campus, like the fireplace smoke that clings to the leather chairs in the hoary library. Compared to this place, the Ritz-Carlton is a kibbutz.