The Facebook photo application for the DSi was first detailed back at E3. While slated for "Fall" in the States, the app has gone live in Japan with a recent firmware update.
It looks like this and allows DSi owners to upload their DSi Album pics on their Facebook page. Since Facebook isn't as popular in Japan as other social networking sites like Mixi, it'll be interesting to see whether this app has any impact on stirring up interest in Facebook.
Though joining Facebook just to upload low-res DSi pics?