I'm concerned about performance too, especially since I use this on forums which have many repeat visitors. One idea I've thought of as an easy fix is setting a cookie the first time the visitor views the site and we have to check where the IP is located. If the IP is in the US, we set the cookie like setcookie("Location", "United States") or setcookie("Location", "International") Then just check $_COOKIE['cookiename'] == "United States" to determine which ads to show on future page loads.
Yahoo wants quality US traffic. So i guess it is right that they are not showing the ads for international traffic.
Can't we just do an IF statement? IF U.S. then show YPN ads ELSE Adsense without all the countries and everything, that would be the fastest I would think.