A used one? I don't think it's been out long enough for there to be a lot of dsi's on the market already.They're $170, but you can find a cheaper, used one that might look new on Ebay
Well, obviously playing games, taking pix with the two cameras.Also, it has a sound system thingy :) and that's used for recording things. It has internet that you can download from the DSi shop on...