Yup, there are stats here: http://ux.stackexchange.com/questions/11363/do-promo-codes-or-coupon-codes-do-more-harm-than-good http://ux.stackexchange.com/questio

Yup, there are stats here: http://ux.stackexchange.com/questions/11363/do-promo-codes-or-coupon-codes-do-more-harm-than-good http://ux.stackexchange.com/questions/11363/do-promo-codes-o... "In one usability test, removing the coupon code field increased overall conversion from 3.8% to 5.1% (an increase of 34%)."