The 3DS can play 3DS games, DS games, it can play 3D movies. What else can it do? How about video chat. In 3D.
In an interview with Forbes magazine, Nintendo president Satoru Iwata said "Technologically speaking, a variety of different things are possible with the 3DS, for example, 3-D video chat."
Interesting. Not sure how that'd work, what with the 3D cameras on the outside, but hey, dream on, Mr. Iwata. It'd make for a nice tech demo, but since this is Nintendo (and also because 3D cameras aren't exactly common), it's likely you'd only be able to use it to communicate with other 3DS owners, reducing its usefulness.
Besides, they say the camera adds ten pounds in two dimensions. The third dimension may not be worth the self-loathing.
Nintendo's Game Changer [Forbes]