Just now, at the Nintendo Developers' Roundtable -- an apparent follow-up to yesterday's keynote -- Katsuya Eguchi announced that not only will players be able to transfer their characters and accumulated items from the DS version of Animal Crossing to the newly announced Animal Crossing: City Folk, but DS-Wii connectivity will feature in other ways as well. While we don't know all of the specifics (we tried to get clarification, but the Q&A wrapped too quickly), it sounds as though you can also use the DS to transfer AC data between Wiis if you don't have Wi-Fi.
Also planned for Japan (for now) is the use of DS Download Stations. Players will be able to download information to their handhelds and take it home for transfer to the Wii title. Sounds like this is meant to open up new buyable items, and Eguchi said they were hoping to bring that feature to the U.S. as well.