Via their new Wi-Fi Connection hub, NintendoWiFi.com, Nintendo has revealed that the upcoming Animal Crossing: Wild World will permit you to receive special letters containing presents from Nintendo.
It is unclear whether the presents constitute downloadable content or not; true downloadable content would add more items to the game, whereas traditionally Nintendo has only offered unlockable items, unlocked by a code they reveal at a later date. You'll be able to opt out of the letters if you wish by using the telephone in your room to set your communication options.
Nintendo has also revealed that Blanca, the cat with a whiteboard for a face (previously seen in Animal Crossing on the train ride between towns) will randomly appear in towns, exhibiting a face drawn by another Wild World player in another town (it is unclear whether this will be restricted to players on one's friend list or whether it will be globally accessible.) Nintendo plans to post some of the Blanca-based works of art on their site.