To the common eye, DSi could look identical to the DS Lite. Nintendo clearly doesn't want that, so it's released a video that runs through each and every feature.
It's great - you get a nice lengthy look at all the new menus, the wacky camera functionality, some of the crazy sound-bending stuff it can do to music or your voice, the DSi shop, the new PictoChat and more.
It's so comprehensive you won't even mind that it's all in Japanese (soz). Anyway, take a look here.