> Basically, it's tied to your DS with your copy of Mario
> Kart, from what I understand. Meaning, my 'friends code'
> will probably change if I actually buy a copy of Mario Kart,
> rather than just rent it.
Not really. It's determined when you first connect your DS to the WFC service, and then it's stored in the DS after that. So, if you rent it, then connect again with a purchased copy, you'll have the same Friend Code. It's (from what I understand) created when the DS connects, and is generated against the MAC address of the device. I haven't tried clearing my WFC data yet, so I dunno if it changes, however. Each copy of Mairo Kart, outside of the SRAM when you play, is identical, though.