Nintendo really wants to know how you feel about The Legend of Zelda: Phantom Hourglass. Or, rather, if this survey is anything like the Brain Age 2 survey, they want to know if there are any non-gamers in the house to whom you can evangelize the game. In any case, they're willing to pay handsomely in single pieces of plastic for the information.
Registering your game and filling out the survey will make you eligible for this cute "Feather Pen Stylus." Really, it's a free thing requiring minimal effort, so why not? You can choose whether or not to poke at your DS with it.