Nintendo president Satoru Iwata gave an interview about the upcoming Wii console to NikkeiBP's Tech-On!, published last week. In it, he reveals one very interesting possibility for the Wii Connect24 service.
"Let's say your Wii is connected to the Internet in a mode that allows activation on a 24-hour basis," Iwata explained. "This would allow Nintendo to send monthly promotional demos for the DS, during the night, to the Wii consoles in each household. Users would wake up each morning, find the LED lamp on their Wii flashing, and know that Nintendo has sent them something. They would then be able to download the promotional demo from their Wii's to their Nintendo DS's. This will, of course, be possible in gaming stores too, but I think users will enjoy being able to do this within their homes. The key merit here is having promotional material delivered to your home, instead of having to go collect it yourself."
Downloadable DS demos have been available in Japan for a long time, and have recently been made available at select retailers in the US at DS Download Stations. The Wii Connect24 service is a special mode of the upcoming Wii console that allows it to remain online while "off", allowing games like the announced Animal Crossing sequel to communicate with other players, as well as allowing game developers to provide new content.