"what exactly does adding a 3DS code do? does anything exciting happen, or is it just for kicks?"
Just like with the Wii System Code, eventually (after a future update) your 3DS's will keep in touch with all your friends consoles, while you are away (when you put your console to sleep and or to charge) which means you might have new challenges to beat on your favorite game.
Unlike the DS and Wii however, the 3DS uses one code for all, in otherwords, if you have JoeBloggs 3DS game code, and you both get Animal Crossing 3DS, you will immediatly become friends in that game, no need to swap a whole new code.
And if you seen the "Friend Code" tool on this site, you can probably see how better it will be just to have one code per system.
I am willing to swap codes with friendly players, and hope to actually have some games with and what not, when the game lineup sparks up. (ready for MK3DS and AC3DS!)
Signature-------------- MMORPG Player! (Final Fantasy XI & Getting Back onto XIV)
Signature-------------- xbox gamertag ZombieCakez message me if you want to play PSN ID ZomieCakez 3DS is the best handheld ;) Wii u ID ZombieCakez = add me
Signature-------------- I'm sorry Mario, but the soap is in the other bathroom. I HEAR VOICES IN MY HEAD, THEY COUNCIL ME THEY UNDERSTAND THEY TALK TO MEE!
how many FC you can have registered in your 3DS?, I really want to know because I´m getting my 3DS this Saturday
Signature-------------- "So, you mind if I sit here? I promise I won't fall asleep, tumble onto you and start drooling on your shirt!" ~ Meeting Rover in the train
Well all i know is more than 10 xD i only have 10 soo, i doubt anyone has a full roster
Signature-------------- I'm sorry Mario, but the soap is in the other bathroom. I HEAR VOICES IN MY HEAD, THEY COUNCIL ME THEY UNDERSTAND THEY TALK TO MEE!