Club Nintendo, because the reward values are changing as of July 1. Completing registration surveys for the Nintendo DSi or Nintendo DSi XL will yield only 100 coins, as opposed to the previously established 160 coins.
Software rewards are also getting a shake-up, though only select titles will see a decrease. Completing registration surveys for some 3D Classics and other downloadable titles will grant fewer coins; however, a lot of first-party 3DS games like Mario Kart 7 and some third-party ones, such as Resident Evil Revelations, are seeing increases. Wii and DS/DSi games are sadly seeing a reduction pretty much across the board. Better put in your Animal Crossing: City Folk code before time runs out!