Let us not forget the famous 'Getting Out More' promo from US Air. After 9/11, US Air was offering a double miles (status and regular) promo and sending individual codes to flyers for this. It turned out the codes were stackable and we were sharing them. I was using multiple codes and receiving 6x miles for trips. Flying out of BTV at that time, it was possible to become Chairman's Preferred by flying 3 RT of BTV-PHL-SFO. Total cost of about $700.