I realize the following video verges dangerously close on commercial territory, but considering the product in question--Flipnote Studio--is a free download on the DSi Shop, I guess we can let it slide. This animation was done in Flipnote by Aardman Animations, the folks responsible for Wallace & Gromit, so they probably know a thing or two about stop-motion animation. (Your results may vary.)
You can see some other, less impressive sample videos and find out about the Flipnote sharing system over on Nintendo's official site.
I felt compelled to post this mostly because I have such fond memories of flexing my primitive nine-frame creativity at my neighbor's house in Mario Paint back in our misspent youths. The movies we cranked out were certainly much cruder (in every sense of the word) than what you can apparently pull off in Flipnote. It's still great to see Nintendo pushing this sort of wacky creative tool on the youth of today.