There are quite a few better 3D cameras on the market currently. The camera in the 3DS is arguably the worst in any device, but it is still a device that many will have who would not have purchased a dedicated 3D camera. It will be their first forray into 3D photography which can be a lot of fun.
Personally, the 3D camera was the feature I had the most fun playing with when I received my 3DS, despite the low quality images, to the point where I did a fair amount of researching into dedicated consumer 3D cameras.
The only current issue is what display are you going to view those 3D images on? Real simple with the 3DS, otherwise 3D cameras really only make sense for those with full sized 3D displays and since I just don't see myself putting on a pair of shutter glasses every time I want to view 3D photos... we're still a ways off from it being as practical as regular digital photography.
As far as the 3DS goes, it's a simple issue of sensor light sensitivity, or maybe the lack there of would be a better way to describe it. If you're not shooting in near daylight levels of brightness, the increased gain results in pretty horrendous color artifacts that are only slightly obscured by being viewed on the low res 3DS display. View the jpegs on any full res display and they become pretty blaring.
