So is it a medium? A platform? I was thinking of using the DS as a datacapture device by having free-play sessions in shopping malls with a prompt at the end of the session. The devices are networked to a central controller so you could monitor what each person was up to.
I can imagine a new kind of shopping mall interaction. Instead of wearing a silly uniform and handing out fliers, the on-site person could invite shoppers to join a networked play (peppered with suitable calls to action or themed to match campaign).