Sometimes you get dinged, sometimes not. My last trip to LHR I got dinged on BA on the connection to Geneva, but not on the return (BA) coming back ten days later. It's brutally expensive, so I do anything I can to avoid the surcharge. I think that BA is much more forgiving if your international leg was also on BA. I carry a lot of mountain climbing gear with me, so the heavy stuff I put in my carry on backpack. Then I stuff as much as possible of the remaining heavy stuff in my carry on. Also, duffel bags can be almost five pounds lighter than rolling suitcases, so that's a little savings.